Improve Gradle build scripts

api/build.gradle

@@ -1,17 +1,3 @@
-plugins {
-    id 'java'
-    id 'org.jetbrains.kotlin.jvm'
-}
-
-group 'io.bartek'
-version '1.0-SNAPSHOT'
-
-sourceCompatibility = 1.8
-
-repositories {
-    mavenCentral()
-}
-
 dependencies {
     implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8"
     testCompile group: 'junit', name: 'junit', version: '4.12'
@@ -20,9 +6,3 @@ dependencies {
     }
 }
 
-compileKotlin {
-    kotlinOptions.jvmTarget = "1.8"
-}
-compileTestKotlin {
-    kotlinOptions.jvmTarget = "1.8"
-}