OneJar plugin fails in Gradle 4.6

[nsoft]

More bit-rot relating to #92

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':oneJar'.
> Cannot convert the provided notation to a File or URI: java.io.BufferedWriter@39d88fd9.
  The following types/formats are supported:
    - A String or CharSequence path, for example 'src/main/java' or '/usr/include'.
    - A String or CharSequence URI, for example 'file:/usr/include'.
    - A File instance.
    - A Path instance.
    - A Directory instance.
    - A RegularFile instance.
    - A URI or URL instance.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

Deprecated Gradle features were used in this build, making it incompatible with Gradle 5.0.
See https://docs.gradle.org/4.6/userguide/command_line_interface.html#sec:command_line_warnings

BUILD FAILED in 1s
4 actionable tasks: 2 executed, 2 up-to-date

[nsoft]

rholder/gradle-one-jar#34

[nsoft]

Fixed in #129