Cleanup headers

Change-Id: I9124366b2000cad54966fb6936bb4691bbf115a3
diff --git a/native/jni/src/unigram_dictionary.cpp b/native/jni/src/unigram_dictionary.cpp
index ce3108b..b2fc870 100644
--- a/native/jni/src/unigram_dictionary.cpp
+++ b/native/jni/src/unigram_dictionary.cpp
@@ -14,8 +14,8 @@
  * limitations under the License.
  */
 
-#include <assert.h>
-#include <string.h>
+#include <cassert>
+#include <cstring>
 
 #define LOG_TAG "LatinIME: unigram_dictionary.cpp"