Fix war file path as argument for jetty runner

[JesseChavez]

This fix the war file path that is given to the embedded Jetty runner.

Before this change:
(only works in older jetty version older than 9.4.32.v20200930)

invoking webserver with:
[--host, 0.0.0.0, --port, 8080, --config, jar:file:/D:/workbench/samson.war!/WEB-INF/webserver.xml, /D:/workbench/samson.war]

After this change:
(works for newer jetty versions starting with 9.4.32.v20200930, includes jetty 10.x)

invoking webserver with:
[--host, 0.0.0.0, --port, 8080, --config, jar:file:/D:/workbench/samson.war!/WEB-INF/webserver.xml, D:\workbench\samson.war]

[JesseChavez]

No sure if I have to commit the generated jar file lib/warbler_jar.jar

[kares]

LGTM, the .jar commit should not be necessary (unfortunately it kind of is atm).

The .jar changes so rarely that it's not part of rake release to rake build the .jar.
But I think it's also a feature as it allows using Warbler from github: 'jruby/warbler' git.

For security reasons and to make sure compilation happens with the tools (Java version) intended it's best if it's performed by a maintainer (as a follow up of merging the PR).

[olleolleolle]

Thanks @JesseChavez!

Thanks @kares for a clear review!

I will make a sign-post Issue about "regenerate the JAR".