GetCommand conditionally adds a filter (implemented as inline Ruby code
in the command line) to transform some of the problematic
Rails-specific eRuby syntax. Specifically, <%= tags are replaced with
<%.
This does not reduce the effectiveness of the linter, because the
transformed code is still evaluated.
This solution was suggested by @rgo at
https://github.com/w0rp/ale/issues/580#issuecomment-337676607.
