Use mavenCentral instead of jscenter for Android example app (#317)

* Use full address for maven in build.gradle

According to:
react-native-camera/react-native-camera#2490 (comment)
the fix for failing build with maven issues is to use the full address
of jitpack.
This commit changes it to example build.gradle.

* Use mavenCentral instead of JCenter

Author: BartoszKlonowski

example/android/build.gradle

@@ -9,7 +9,7 @@ buildscript {
     }
     repositories {
         google()
-        jcenter()
+        mavenCentral()
     }
     dependencies {
         classpath("com.android.tools.build:gradle:4.1.0")
@@ -32,7 +32,10 @@ allprojects {
         }
 
         google()
-        jcenter()
-        maven { url 'https://jitpack.io' }
+        mavenCentral()
+        maven {
+            url 'https://maven.google.com/'
+            name 'Google'
+        }
     }
 }