Fix bug in rocketchat - opsdroid wouldn't reply

[FabioRosado]

Description

While working on implementing the Image event I have noticed that opsdroid wasn't replying to a command. This PR fixes this bug and also updates the documentation in regards to images. Which sadly doesn't seem to be able to be implemented with the current API.

Status

READY | UNDER DEVELOPMENT | ON HOLD

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• Documentation (fix or adds documentation)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration.

• Tox - all green
• Sent message to rocket.chat - opsdroid replied successfully

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov]

Codecov Report

Merging #936 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##           master   #936   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          37     37           
  Lines        2342   2342           
=====================================
  Hits         2342   2342

Impacted Files	Coverage Δ
opsdroid/connector/rocketchat/__init__.py	100% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 01ec646...7ef3217. Read the comment docs.

[jacobtomlinson]

Thanks @FabioRosado !