Bump kotlin_version from 1.3.41 to 1.3.50

Bumps `kotlin_version` from 1.3.41 to 1.3.50.

Updates `kotlin-gradle-plugin` from 1.3.41 to 1.3.50
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](https://github.com/JetBrains/kotlin/commits)

Updates `kotlin-stdlib-jdk7` from 1.3.41 to 1.3.50
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](https://github.com/JetBrains/kotlin/commits)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

build.gradle

@@ -7,7 +7,7 @@
 import com.github.spotbugs.SpotBugsTask
 
 buildscript {
-    ext.kotlin_version = '1.3.41'
+    ext.kotlin_version = '1.3.50'
     repositories {
         google()
         jcenter()