Update Gradle wrapper to Gradle version 4.4.1

[saschpe]

Provides much faster builds

See: https://docs.gradle.org/4.4.1/release-notes.html
See: https://docs.gradle.org/4.3.1/release-notes.html
See: https://docs.gradle.org/4.2.1/release-notes.html

[saschpe]

Mhm, not much happening here.

[dmfs]

@lemonboston please review

[lemonboston]

Looks good, thanks.