Upgrade images in .drone.yml to more recent versions

[techknowlogick]

This builds Gitea with go 1.11, and upgrades alpine to 3.7

Note: As this uses golang 1.11 for the make fmt check it does a different check and so developers need to be aware of this when doing the check.

[codecov-io]

Codecov Report

Merging #4819 into master will increase coverage by 16.52%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           master    #4819       +/-   ##
===========================================
+ Coverage   20.69%   37.21%   +16.52%     
===========================================
  Files         167      305      +138     
  Lines       32389    45041    +12652     
===========================================
+ Hits         6702    16764    +10062     
- Misses      24706    25840     +1134     
- Partials      981     2437     +1456

Impacted Files	Coverage Δ
modules/templates/helper.go	49.84% <ø> (ø)
modules/markup/html.go	89.59% <100%> (+9.69%)	⬆️
models/migrations/v60.go	0% <0%> (ø)
routers/api/v1/org/hook.go	0% <0%> (ø)
modules/public/dynamic.go	100% <0%> (ø)
modules/httplib/httplib.go	25.44% <0%> (ø)
models/migrations/v65.go	0% <0%> (ø)
routers/admin/admin.go	0% <0%> (ø)
routers/api/v1/org/member.go	0% <0%> (ø)
routers/init.go	75% <0%> (ø)
... and 229 more

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