Fix docs deployment

[navidcy]

This PR removes cap on Documenter and fixes deprecations for docs deployment.

[coveralls]

Pull Request Test Coverage Report for Build 274

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 98.441%

---

Totals
Change from base Build 270:	0.0%
Covered Lines:	505
Relevant Lines:	513

---

💛 - Coveralls

[codecov]

Codecov Report

Merging #31 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #31   +/-   ##
=======================================
  Coverage   98.44%   98.44%           
=======================================
  Files           6        6           
  Lines         513      513           
=======================================
  Hits          505      505           
  Misses          8        8

---

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 7ab52d1...377d18f. Read the comment docs.

[navidcy]

@glwagner, I'm merging this.