Gradle无法解析Android Studio中的库

我想在Android Studio中包含一个库，但显示如下错误：

“无法解决：com.lemonlab：expandable-button-menu：1.0.0”

如何解决这个问题？

    apply plugin: 'com.android.application'

    android {
        compileSdkVersion 21
        buildToolsVersion '21.1.2'

        defaultConfig {
            applicationId "ayowes.com.newecampus"
            minSdkVersion 15
            targetSdkVersion 21
            versionCode 1
            versionName "1.0"
        }
        buildTypes {
            release {
                minifyEnabled false
                proguardFiles getDefaultProguardFile('proguard-android-ptimize.txt'), 'proguard-rules.txt'
            }
        }
    }

    dependencies {
        compile fileTree(dir: 'libs', include: ['*.jar'])
        compile 'com.android.support:appcompat-v7:21.0.3'
        compile 'com.google.android.gms:play-services:6.5.87'
        compile 'com.lemonlab:expandable-button-menu:1.0.0'
        compile files('libs/pinchzoom.jar')
    }