Fix style of YARD @return tag description

Before there was lots of redundant information. These comments where
very old and my current YARD doc style changed in the meantime. Keep it
DRY.

lib/mutant/cli.rb

@@ -19,7 +19,7 @@ module Mutant
     # @param [Array<String>] arguments
     #
     # @return [Fixnum]
-    #   returns exit status
+    #   the exit status
     #
     # @api private
     #

lib/mutant/color.rb

@@ -36,7 +36,7 @@ module Mutant
       # @param [String] text
       #
       # @return [String]
-      #   returns the argument string
+      #   the argument string
       #
       # @api private
       #

lib/mutant/differ.rb

@@ -108,7 +108,6 @@ module Mutant
     # @param [String] line
     #
     # @return [String]
-    #   returns colorized line
     #
     # @api private
     #

lib/mutant/matcher/chain.rb

@@ -9,10 +9,10 @@ module Mutant
       # Enumerate subjects
       #
       # @return [Enumerator<Subject]
-      #   returns subject enumerator if no block given
+      #   if no block given
       #
       # @return [self]
-      #   returnns self otherwise
+      #   otherwise
       #
       # @api private
       #

lib/mutant/matcher/method.rb

@@ -14,10 +14,10 @@ module Mutant
       # Enumerate matches
       #
       # @return [Enumerable<Subject>]
-      #   returns enumerable when no block given
+      #   if no block given
       #
       # @return [self]
-      #   returns self when block given
+      #   otherwise
       #
       # @api private
       #
@@ -129,7 +129,7 @@ module Mutant
       # Return subject
       #
       # @return [Subject]
-      #   returns subject if there is a matched node
+      #   if there is a matched node
       #
       # @return [nil]
       #   otherwise

lib/mutant/matcher/method/instance.rb

@@ -45,10 +45,10 @@ module Mutant
         # @param [Parser::AST::Node] node
         #
         # @return [true]
-        #   returns true if node matches method
+        #   if node matches method
         #
         # @return [false]
-        #   returns false if node NOT matches method
+        #   otherwise
         #
         # @api private
         #

lib/mutant/predicate.rb

@@ -28,7 +28,7 @@ module Mutant
     #   when can be build from string
     #
     # @return [nil]
-    #   returns nil otherwise
+    #   otherwise
     #
     # @api private
     #
@@ -46,7 +46,6 @@ module Mutant
     # @param [String] _notation
     #
     # @return [nil]
-    #   returns nil
     #
     # @api private
     #
@@ -62,7 +61,6 @@ module Mutant
       # @pram [Mutation] _mutation
       #
       # @return [true]
-      #   returns true
       #
       # @api private
       #

lib/mutant/reporter/cli/printer.rb

@@ -164,10 +164,10 @@ module Mutant
         # Test for colored output
         #
         # @return [true]
-        #   returns true if output is colored
+        #   if output is colored
         #
         # @return [false]
-        #   returns false otherwise
+        #   otherwise
         #
         # @api private
         #
@@ -183,8 +183,8 @@ module Mutant
         # @api private
         #
         # @return [String]
-        #   returns colorized string if color is enabled
-        #   returns unmodified message otherwise
+        #   if color is enabled
+        #   unmodified message otherwise
         #
         def colorize(color, message)
           color = Color::NONE unless tty?
@@ -194,10 +194,10 @@ module Mutant
         # Test for output to tty
         #
         # @return [true]
-        #   returns true if output is a tty
+        #   if output is a tty
         #
         # @return [false]
-        #   returns false otherwise
+        #   otherwise
         #
         # @api private
         #

lib/mutant/support/method_object.rb

@@ -23,7 +23,6 @@ module Mutant
     # Not aliased to prevent problems from inheritance
     #
     # @return [Objecct]
-    #   returns the created object
     #
     # @api private
     #