Add erubis linter

This linter works largely the same as the existing `erubylint` linter,
except it works with `erubis` instead of `erb` as the driving command.

ale_linters/eruby/erubis.vim

@@ -0,0 +1,11 @@
+" Author: Jake Zimmerman <jake@zimmerman.io>
+" Description: eruby checker using `erubis`, instead of `erb`
+
+call ale#linter#Define('eruby', {
+\   'name': 'erubis',
+\   'executable': 'erubis',
+\   'output_stream': 'stderr',
+\   'command': 'erubis -x %t | ruby -c',
+\   'callback': 'ale#handlers#ruby#HandleSyntaxErrors',
+\})
+