Fix missing comma in core.gypi

Source/core/core.gypi

 {
     'includes': [
         'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/KeyframeEffect.idl',
             'animation/EffectModel.idl',
             'animation/AnimationEffectReadOnly.idl',
@@ skipping 1118 matching lines @@
             'css/FontFaceSet.cpp',
             'css/FontFaceSet.h',
             'css/FontFaceSetForEachCallback.h',
             'css/FontFaceSetLoadEvent.cpp',
             'css/FontFaceSetLoadEvent.h',
             'css/FontLoader.cpp',
             'css/FontLoader.h',
             'css/FontSize.cpp',
             'css/FontSize.h',
             'css/FontStyleMatcher.cpp',
-            'css/FontStyleMatcher.h'
+            'css/FontStyleMatcher.h',
             'css/HashTools.h',
             'css/KeyframeStyleRuleCSSStyleDeclaration.cpp',
             'css/KeyframeStyleRuleCSSStyleDeclaration.h',
             'css/ComputedStyleCSSValueMapping.h',
             'css/ComputedStyleCSSValueMapping.cpp',
             'css/LocalFontFaceSource.cpp',
             'css/LocalFontFaceSource.h',
             'css/MediaList.cpp',
             'css/MediaList.h',
             'css/MediaQuery.cpp',
@@ skipping 2706 matching lines @@
             'style/OutlineValueTest.cpp',
             'style/SVGComputedStyleTest.cpp',
             'svg/UnsafeSVGAttributeSanitizationTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }