build: Allow kotlin-compiler downloading from sonatype

This patch allows one to download the kotlin-compiler dependency
not only from the bintray mirror but also from the sonatype original
repo.

backend.native/build.gradle

@@ -37,9 +37,8 @@ apply plugin: org.jetbrains.kotlin.NativeInteropPlugin
 // (gets applied to this project and all its subprojects)
 allprojects {
     repositories {
-        maven {
-            url 'http://dl.bintray.com/jetbrains/kotlin-native-dependencies'
-        }
+        maven { url 'http://dl.bintray.com/jetbrains/kotlin-native-dependencies' }
+        maven { url 'http://oss.sonatype.org/content/repositories/snapshots' }
     }
 
     configurations.all {

tools/gradle-plugin/build.gradle

@@ -24,9 +24,8 @@ apply plugin: 'com.jfrog.bintray'
 // Copied from backend.native
 allprojects {
     repositories {
-        maven {
-            url 'http://dl.bintray.com/jetbrains/kotlin-native-dependencies'
-        }
+        maven { url 'http://dl.bintray.com/jetbrains/kotlin-native-dependencies' }
+        maven { url 'http://oss.sonatype.org/content/repositories/snapshots' }
     }
 
     configurations.all {

tools/helpers/build.gradle

@@ -33,9 +33,8 @@ buildscript {
 
 // Copied from backend.native project. =====
 repositories {
-    maven {
-        url 'http://dl.bintray.com/jetbrains/kotlin-native-dependencies'
-    }
+    maven { url 'http://dl.bintray.com/jetbrains/kotlin-native-dependencies' }
+    maven { url 'http://oss.sonatype.org/content/repositories/snapshots' }
 }
 
 configurations.all {