upgrade Android gradle plugin

build.gradle

@@ -14,7 +14,7 @@ buildscript {
         google()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.1.2'
+        classpath 'com.android.tools.build:gradle:3.1.3'
         classpath 'com.google.gms:google-services:3.0.0'
         classpath 'org.codehaus.groovy:groovy-all:2.4.12' 
         classpath('com.dicedmelon.gradle:jacoco-android:0.1.2') {