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/v1.3.50/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.3.41...v1.3.50)

Updates `kotlin-stdlib-jdk8` from 1.3.41 to 1.3.50
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.3.50/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.3.41...v1.3.50)

Signed-off-by: dependabot-preview[bot] <[email protected]>

build.gradle

@@ -1,7 +1,7 @@
 import net.researchgate.release.GitAdapter
 
 buildscript {
-    ext.kotlin_version = '1.3.41'
+    ext.kotlin_version = '1.3.50'
     ext.spring_version = '5.1.5.RELEASE'
     ext.jackson_version = '2.9.8'
     ext.thymeleaf_version = '3.0.11.RELEASE'