Fix rubocop warnings in Mutant::Mutator namespace

lib/mutant/mutator/node.rb

@@ -154,7 +154,7 @@ module Mutant
       #
       def emit_child_update(index, node)
         new_children = children.dup
-        new_children[index]=node
+        new_children[index] = node
         emit_self(*new_children)
       end
 

lib/mutant/mutator/node/connective/binary.rb

@@ -11,7 +11,7 @@ module Mutant
             :or  => :and,
           }.freeze
 
-          handle *INVERSE.keys
+          handle(*INVERSE.keys)
 
           children :left, :right
 

lib/mutant/mutator/node/named_value/variable_assignment.rb

@@ -15,7 +15,7 @@ module Mutant
             :lvasgn => ''
           )
 
-          handle *MAP.keys
+          handle(*MAP.keys)
 
         private
 

lib/mutant/mutator/registry.rb

@@ -24,7 +24,7 @@ module Mutant
       #
       def self.register(type, mutator_class)
         raise "duplicate type registration: #{type}" if registry.key?(type)
-        registry[type]=mutator_class
+        registry[type] = mutator_class
         self
       end
 
@@ -42,7 +42,7 @@ module Mutant
       def self.lookup(node)
         type = node.type
         registry.fetch(type) do
-          raise ArgumentError,"No mutator to handle: #{type.inspect}"
+          raise ArgumentError, "No mutator to handle: #{type.inspect}"
         end
       end