[Style] Use single quotes instead

spec/unit/generator/xcconfig/aggregate_xcconfig_spec.rb

@@ -135,11 +135,11 @@ module Pod
           end
 
           it 'adds the framework build path to the xcconfig, with quotes, as framework search paths' do
-            @xcconfig.to_hash['FRAMEWORK_SEARCH_PATHS'].should == "\"$PODS_FRAMEWORK_BUILD_PATH\""
+            @xcconfig.to_hash['FRAMEWORK_SEARCH_PATHS'].should == '"$PODS_FRAMEWORK_BUILD_PATH"'
           end
 
           it 'adds the framework header paths to the xcconfig, with quotes, as local headers' do
-            expected = "$(inherited) -iquote \"$PODS_FRAMEWORK_BUILD_PATH/OrangeFramework.framework/Headers\""
+            expected = '$(inherited) -iquote "$PODS_FRAMEWORK_BUILD_PATH/OrangeFramework.framework/Headers"'
             @xcconfig.to_hash['OTHER_CFLAGS'].should == expected
           end