Add missing import on AirMapModule.java (react-native-maps#1958)

Author: vendramini

lib/android/src/main/java/com/airbnb/android/react/maps/AirMapModule.java

@@ -12,6 +12,7 @@
 import com.facebook.react.bridge.ReactContextBaseJavaModule;
 import com.facebook.react.bridge.ReactMethod;
 import com.facebook.react.bridge.ReadableMap;
+import com.facebook.react.bridge.WritableMap;
 import com.facebook.react.bridge.WritableNativeMap;
 import com.facebook.react.uimanager.NativeViewHierarchyManager;
 import com.facebook.react.uimanager.UIBlock;