Bump gradle-scalafmt version

gradle-scalafmt:1.5.0 was not reachable for about a week while any other tags were accessible.
( https://plugins.gradle.org/m2/gradle/plugin/cz/alenkacz/gradle-scalafmt/1.5.0)

We will not be able to do any gradlew command without any changes.

```bash
./gradlew clean --refresh-dependencies
Build using Scala 2.12

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring root project 'openwhisk'.
> Could not resolve all artifacts for configuration ':classpath'.
> Could not find gradle.plugin.cz.alenkacz:gradle-scalafmt:1.5.0.
Searched in the following locations:
- https://jcenter.bintray.com/gradle/plugin/cz/alenkacz/gradle-scalafmt/1.5.0/gradle-scalafmt-1.5.0.pom
- https://plugins.gradle.org/m2/gradle/plugin/cz/alenkacz/gradle-scalafmt/1.5.0/gradle-scalafmt-1.5.0.pom
Required by:
project :

```