Bump kotlin_version from 1.3.61 to 1.5.21

Bumps `kotlin_version` from 1.3.61 to 1.5.21.

Updates `kotlin-gradle-plugin` from 1.3.61 to 1.5.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.3.61...v1.5.21)

Updates `kotlin-stdlib-jdk7` from 1.3.61 to 1.5.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.3.61...v1.5.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib-jdk7
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

build.gradle

@@ -2,7 +2,7 @@
 
 buildscript {
     apply from: 'dependencies.gradle'
-    ext.kotlin_version = '1.3.61'
+    ext.kotlin_version = '1.5.21'
     repositories {
         google()
         jcenter()