Double dash options are incorrectly passed as commands

[ches]

Recent versions of the OG sbt launcher script accept a number of conventional long-style options such as --no-colors and --supershell=false.

sbt-extras passes these through to sbt as commands that are invalid:

$ sbt --supershell=false
[info] welcome to sbt 1.5.5 (Oracle Corporation Java 1.8.0_202)
[info] loading settings for project global-plugins from plugins.sbt ...
[info] loading global plugins from /Users/ches/.sbt/1.0/plugins
[info] loading settings for project g8-build from plugins.sbt ...
[info] loading project definition from /Users/ches/src/scala/scala-project.g8/target/g8/project
[info] loading settings for project g8 from build.sbt ...
[info] set current project to new-project (in build file:/Users/ches/src/scala/scala-project.g8/target/g8/)
[error] Expected symbol
[error] Not a valid command: --
[error] Expected 'debug'
[error] Expected 'info'
[error] Expected 'warn'
[error] Expected 'error'
[error] Expected 'addPluginSbtFile'
[error] --supershell=false
[error]   ^