Gradle改造未能解决

这是我第一次尝试使用gradle和android项目.我想对我的项目添加改造,但它一直在告诉我.

无法解决:com.squareup.retrofit:retrofit:1.9.0

无法解决:com.squareup.okhttp:2.2.0

但是,谷歌播放服务运作完美.

我的gradle文件如下:

apply plugin: 'com.android.application'

android {
  compileSdkVersion 21
  buildToolsVersion "21.1.2"

  defaultConfig {
    applicationId "test.gradel"
    minSdkVersion 14
    targetSdkVersion 21
    versionCode 1
    versionName "1.0"
 }
 buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
 }
}

dependencies {
  compile fileTree(include: ['*.jar'], dir: 'libs')
  compile 'com.android.support:appcompat-v7:21.0.3'
  compile 'com.google.android.gms:play-services:6.5.87'
  compile group: "com.squareup.retrofit", name: "retrofit", version: "1.9.0"
  compile group: "com.squareup.okhttp", name: "okhttp", version: "2.2.0"
}

buildscript {
  repositories {
    jcenter()
  }

  dependencies {
    classpath 'com.android.tools.build:gradle:1.1.2'
  } 
}

任何帮助将不胜感激.

谢谢