Use standard import syntax (#3083)

Author: paulb777

GoogleUtilities/SwizzlerTestHelpers/GULSwizzler+Unswizzle.m

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#import "../MethodSwizzler/Private/GULSwizzler.h"
+#import <GoogleUtilities/GULSwizzler.h>
 
 #import <objc/runtime.h>