BasicStringRef<T>的difference_type类型改为std::ptrdiff_t;
BasicStringRef<T>的difference_type类型改为std::ptrdiff_t;

Signed-off-by: shines77 <c816ee361b8bcaf7cf19d627e3bc89a63016b2b4@msn.com>

shines77/StringMatch,shines77/StringMatch