Getting Error "Gradle DSL method not found: 'compile()'" when Syncing Build.Gradle

To add V4 support libraries to android studio, i followed this document:https://developer.android.com/tools/support-library/setup.html#libs-without-res but I get an error. Here is what i did

1. SDK manager> Installed Android Support Library and Android Repository.
2. Go to Build.Gradle and added the line as given in the dcoument. Build.Gradle now looks like this:

// Top-level build file where you can add configuration options common to all sub-projects/modules.

buildscript {
repositories {
    jcenter()
}
dependencies {
    classpath 'com.android.tools.build:gradle:0.13.2'

    // NOTE: Do not place your application dependencies here; they belong
    // in the individual module build.gradle files
}
}

allprojects {
repositories {
    jcenter()
    dependencies {

        compile "com.android.support:support-v4:18.0.+"
    }
}

}

Then, I get a popup that suggest that I sync gradle. When i sync Gradle, i get this error:

Error:(20, 0) Gradle DSL method not found: 'compile()' Possible causes:

The project 'staymax' may be using a version of Gradle that does not contain the method. Open Gradle wrapper file

The build file may be missing a Gradle plugin. Apply Gradle plugin

Am i missing any step? Please suggest.

Build.Gradle(app)

apply plugin: 'com.android.application'

android {
compileSdkVersion 20
buildToolsVersion "20.0.0"

defaultConfig {
    applicationId "com.appt.shreyabisht.staymax"
    minSdkVersion 15
    targetSdkVersion 20
    versionCode 1
    versionName "1.0"
}
buildTypes {
    release {
        runProguard false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
 }
}

dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
}