Fix C source code files' type

The correct file type string is `sourcecode.c.c` and not `sourcecode.c`

Author: mbektchiev

lib/pbxFile.js

@@ -3,7 +3,7 @@ var $path = require('path'),
     HEADER_FILE_TYPE_SUFFIX = ".h",
     SOURCE_CODE_FILE_TYPE_PREFIX = "sourcecode.",
     M_EXTENSION = /[.]m$/, SOURCE_FILE = 'sourcecode.c.objc',
-    C_EXTENSION = /[.]c$/, C_SOURCE_FILE = 'sourcecode.c',
+    C_EXTENSION = /[.]c$/, C_SOURCE_FILE = 'sourcecode.c.c',
     H_EXTENSION = /[.]h$/, HEADER_FILE = 'sourcecode.c.h',
     MM_EXTENSION = /[.]mm$/, MM_SOURCE_FILE = 'sourcecode.cpp.objcpp',
     HPP_EXTENSION = /[.](hpp|hxx|h\+\+|hh)$/, CPP_HEADER_FILE = 'sourcecode.cpp.h',