Plugin Error : Spek threw an uncaught TypeCastException.

[ManaliN]

I am new to Kotlin and Spek. I am trying to setup Spek with kotlin-android for BDD Testing.
I have added the following in the build.gradle:

apply plugin: 'kotlin-android'

apply plugin: 'kotlin-android-extensions'

// Repository required for Unit Testing
repositories {
maven { url "http://dl.bintray.com/jetbrains/spek" }
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:26.1.0'
implementation 'com.android.support.constraint:constraint-layout:1.0.2'
testImplementation 'junit:junit:4.12'
androidTestImplementation('com.android.support.test.espresso:espresso-core:3.0.1', {
exclude group: 'com.android.support', module: 'support-annotations'
})
implementation"org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"

// Unit Test Specific dependencies
testCompile 'org.jetbrains.spek:spek-api:1.1.0-beta3'
testCompile 'org.jetbrains.spek:spek-junit-platform-engine:1.1.0-beta3'
testCompile 'org.junit.platform:junit-platform-runner:1.0.1'
testCompile 'org.mockito:mockito-core:2.7.5'
testCompile "com.nhaarman:mockito-kotlin:1.3.0"
testCompile "org.jetbrains.kotlin:kotlin-test:$kotlin_version"
testCompile "org.jetbrains.kotlin:kotlin-test-junit:$kotlin_version"

}

I have added the following example test:

import org.jetbrains.spek.api.Spek
import org.jetbrains.spek.api.dsl.given
import org.jetbrains.spek.api.dsl.it
import org.jetbrains.spek.api.dsl.on

import kotlin.test.assertEquals

class ExampleUnitTest : Spek( {
given("Two numbers") {
val firstNumber = 3
val secondNumber = 5
on("adding the numbers") {
val result = firstNumber + secondNumber
it("should return the correct sum") {
assertEquals(8, result)
}
}
}

})

On building the project, I'm getting a Plugin Error, Spek threw an uncaught TypeCastException, which only gives option of disabling the Plugin.

Can anyone please help in setting up the Spek tool for Android with Kotlin?
Thanks a lot in advance!