Doc fixes [ci skip]

activesupport/lib/active_support/core_ext/hash/slice.rb

@@ -1,5 +1,5 @@
 class Hash
-  # Slice a hash to include only the given keys. Returns a hash containing 
+  # Slices a hash to include only the given keys. Returns a hash containing 
   # the given keys.
   # 
   #   { a: 1, b: 2, c: 3, d: 4 }.slice(:a, :b)

activesupport/lib/active_support/core_ext/string/behavior.rb

@@ -1,5 +1,5 @@
 class String
-  # Enable more predictable duck-typing on String-like classes. See <tt>Object#acts_like?</tt>.
+  # Enables more predictable duck-typing on String-like classes. See <tt>Object#acts_like?</tt>.
   def acts_like_string?
     true
   end

activesupport/lib/active_support/core_ext/string/inflections.rb

@@ -178,7 +178,7 @@ class String
     ActiveSupport::Inflector.tableize(self)
   end
 
-  # Create a class name from a plural table name like Rails does for table names to models.
+  # Creates a class name from a plural table name like Rails does for table names to models.
   # Note that this returns a string and not a class. (To convert to an actual class
   # follow +classify+ with +constantize+.)
   #

activesupport/lib/active_support/core_ext/string/multibyte.rb

@@ -35,7 +35,7 @@ class String
     ActiveSupport::Multibyte.proxy_class.new(self)
   end
 
-  # Return +true+ if string has utf_8 encoding.
+  # Returns +true+ if string has utf_8 encoding.
   #
   #   utf_8_str = "some string".encode "UTF-8"
   #   iso_str = "some string".encode "ISO-8859-1"