Add maven proxy configuration.

Fixes #12

Author: vkryachko

buildSrc/build.gradle

@@ -17,6 +17,11 @@ plugins {
 }
 
 repositories {
+    if (System.getenv().containsKey("FIREBASE_CI")) {
+        maven {
+            url "http://maven-proxy/"
+        }
+    }
     maven {
         url 'https://maven.google.com/'
     }

root-project.gradle

@@ -18,6 +18,11 @@ import groovy.io.FileType
 buildscript {
 
     repositories {
+        if (System.getenv().containsKey("FIREBASE_CI")) {
+            maven {
+                url "http://maven-proxy/"
+            }
+        }
         google()
         jcenter()
         mavenCentral()
@@ -47,6 +52,11 @@ apply plugin: com.google.firebase.gradle.plugins.publish.PublishingPlugin
 
 configure(subprojects) {
     repositories {
+        if (System.getenv().containsKey("FIREBASE_CI")) {
+            maven {
+                url "http://maven-proxy/"
+            }
+        }
         google()
         jcenter()
         mavenLocal()