Cleanup headers

Change-Id: I9124366b2000cad54966fb6936bb4691bbf115a3
diff --git a/native/jni/src/bigram_dictionary.cpp b/native/jni/src/bigram_dictionary.cpp
index 8dc21220..bc34e4e 100644
--- a/native/jni/src/bigram_dictionary.cpp
+++ b/native/jni/src/bigram_dictionary.cpp
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#include <string.h>
+#include <cstring>
 
 #define LOG_TAG "LatinIME: bigram_dictionary.cpp"