Apply correct cflags to source files

Using -std=c++0x is sufficient to compile libsass

binding.gyp

@@ -83,14 +83,8 @@
           ]
         }],
         ['OS!="win"', {
-          'cflags+': [
-            '-std=c++11'
-          ],
-          'cflags_c+': [
-            '-std=c++11'
-          ],
           'cflags_cc+': [
-            '-std=c++11'
+            '-std=c++0x'
           ]
         }]
       ]