Fix some whitespace issues

spec/support/mutation_verifier.rb

@@ -93,4 +93,3 @@ private
   end
   memoize :unparser
 end # MutationVerifier
-

spec/unit/mutant/mutator/node/named_value/access_spec.rb

@@ -61,7 +61,7 @@ describe Mutant::Mutator::Node::NamedValue::Access, 'mutations' do
       mutants << 'a = nil; nil'
       mutants << 'a = nil'
       mutants << 'a = ::Object.new; a'
-      # TODO:
+      # TODO: fix invalid AST
       #   These ASTs are not valid and should NOT be emitted
       #   Mutations of lvarasgn need to be special cased to avoid this.
       mutants << s(:begin, s(:lvasgn, :srandom, s(:nil)), s(:lvar, :a))

spec/unit/mutant/mutator/node/op_assgn_spec.rb

@@ -16,7 +16,7 @@ describe Mutant::Mutator::Node::Generic, 'op_asgn' do
     mutations << '@a.b += 5'
     mutations << 'nil.b += 1'
     mutations << 'nil'
-    # TODO:
+    # TODO: fix invalid AST
     #   This should not get emitted as invalid AST with valid unparsed source
     mutations << s(:op_asgn, s(:ivar, :@a), :+, s(:int, 1))
   end