Add missing newline at the end of gf_lexing.h.

contrib/c-bindings/gf_lexing.h

@@ -23,4 +23,4 @@ typedef char *(*GF_StringOp)(const char *str);
 
 /* Returns a GF_StringOp applying the operation op if available, otherwise
    NULL. op is assumed to be non-NULL. The GF_StringOp MUST NOT be freed. */
-GF_StringOp gf_stringOp(const char *op);
+GF_StringOp gf_stringOp(const char *op);