Move maven repository declaration

- Remove redundant jcenter (already included in the "global application" build.gradle)

app/build.gradle

@@ -1,12 +1,5 @@
 apply plugin: 'com.android.application'
 
-allprojects {
-    repositories {
-        jcenter()
-        maven { url 'https://maven.google.com' }
-    }
-}
-
 android {
     compileSdkVersion 26
     buildToolsVersion '26.0.1'

build.gradle

@@ -15,5 +15,6 @@ buildscript {
 allprojects {
     repositories {
         jcenter()
+        maven { url 'https://maven.google.com' }
     }
 }