gradle: use version 4.5

Change-Id: I67564d49f34bf737a1f959dc8bae267c38d7d408

ring-android/build.gradle

@@ -4,7 +4,7 @@ buildscript {
         google()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.1.1'
+        classpath 'com.android.tools.build:gradle:3.1.2'
         classpath 'com.google.gms:google-services:3.1.1'
     }
 }
@@ -16,5 +16,5 @@ allprojects {
 }
 
 task wrapper(type: Wrapper) {
-    gradleVersion = '4.6' //version required
+    gradleVersion = '4.5' //version required
 }

ring-android/gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.6-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.5-all.zip