build(deps): bump kotlin-stdlib-jdk7 from 1.6.20 to 1.6.21 in /android

Bumps [kotlin-stdlib-jdk7](https://github.com/JetBrains/kotlin) from 1.6.20 to 1.6.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.6.21/ChangeLog.md)
- [Commits](https://github.com/JetBrains/kotlin/compare/v1.6.20...v1.6.21)

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

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

@@ -2,7 +2,7 @@ group 'dev.steenbakker.mobile_scanner'
 version '1.0-SNAPSHOT'
 
 buildscript {
-    ext.kotlin_version = '1.6.20'
+    ext.kotlin_version = '1.6.21'
     repositories {
         google()
         mavenCentral()