add additional godoc url configuration

[stamblerre]

The user's configured "go_doc_url" variable should still work correctly in the case when the "gogetdoc" command isn't installed.

[codecov-io]

Codecov Report

Merging #1629 into master will decrease coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1629      +/-   ##
==========================================
- Coverage   19.19%   19.17%   -0.02%     
==========================================
  Files          53       53              
  Lines        4153     4156       +3     
==========================================
  Hits          797      797              
- Misses       3356     3359       +3

Flag	Coverage Δ
#nvim	14.53% <0%> (-0.02%)	⬇️
#vim74	17.56% <0%> (-0.02%)	⬇️
#vim80	18.33% <0%> (-0.02%)	⬇️

Impacted Files	Coverage Δ
autoload/go/doc.vim	0% <0%> (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 e0f9c34...8a45bec. Read the comment docs.

[fatih]

Hi @stamblerre

Seems like this is still missing things? I dont' see the actual fix you describe in the commit message. I assume you want to move out the gogetdoc check from the go#doc#OpenBrowser() function however this PR doesn't include it. Let me know if I miss something.

[stamblerre]

Sorry, I probably wasn't very clear in the message. I just wanted to change the place on line 64 where "https://godoc.org/" was still hardcoded.

[fatih]

This looks good. The only small thing would is the function signature. In Vim script we use snake_case, but I'll do that after merging. Thanks @stamblerre