Remove value from LinkButtonElement

[pedromcaraujo]

Summary

Fixes #562

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #563 into master will increase coverage by 0.03%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master     #563      +/-   ##
==========================================
+ Coverage   68.81%   68.84%   +0.03%     
==========================================
  Files          15       15              
  Lines        1725     1730       +5     
  Branches       98       99       +1     
==========================================
+ Hits         1187     1191       +4     
  Misses        512      512              
- Partials       26       27       +1

Impacted Files	Coverage Δ
slack/web/classes/elements.py	85.39% <80%> (-0.16%)	⬇️

---

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 687695b...d69276b. Read the comment docs.

[RodneyU215]

Thank you @pedroma! For reporting the issue and even more so for submitting a PR to fix it. 🙇

[pedromcaraujo]

Thank you! *Pedro Araújo* FOUNDER & CTO, ATTENTIVE.US <http://attentive.us/> +351967814908 *Check out our new blog - Contextual Sales <http://blog.attentive.us/>*

…

On Thu, Nov 21, 2019 at 4:33 AM Rodney Urquhart ***@***.***> wrote: Thank you @pedroma <https://github.com/pedroma>! For reporting the issue and even more so for submitting a PR to fix it. 🙇 — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#563>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAB5Z3ECOIMZQKUMWZV55E3QUYFSNANCNFSM4JNZLT4A> .