fixed kotlin plugin declaration

Author: Wicpar

build.gradle

@@ -1,17 +1,5 @@
-buildscript {
-    repositories {
-        maven {
-            url "https://plugins.gradle.org/m2/"
-        }
-    }
-
-    dependencies {
-        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
-    }
-}
-
 plugins {
-    id 'org.jetbrains.kotlin.jvm'
+    id 'org.jetbrains.kotlin.jvm' version '1.3.61'
 }
 
 group 'com.papsign.ktor'