Parser doesn't always backtrack

[Riscky]

I noticed that the Hoff parser doesn't backtrack when one of the environments or subprojects is a prefix of another.

For example, lets configure two environments staging and staging_new. One can now use @hoff merge and deploy to staging, but when one tries to use @hoff merge and deploy to staging_new, the parser fails to backtrack, and greets you with:

Unknown or invalid command found:

    comment:1:33:
      |
    1 | @OpsBotPrime merge and deploy to staging_new
      |                                         ^
    Merge commands may not be followed by anything other than a punctuation character ('.', ',', '!', '?', ':', ';').

[Riscky]

Fixed by #257