supress doc-generation in CI if base is not master

[ablaom]

No description provided.

[codecov-io]

Codecov Report

Merging #59 (32b7181) into master (d54f4e0) will decrease coverage by 0.18%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #59      +/-   ##
==========================================
- Coverage   98.91%   98.72%   -0.19%     
==========================================
  Files           7        7              
  Lines         277      236      -41     
==========================================
- Hits          274      233      -41     
  Misses          3        3              

Impacted Files	Coverage Δ
src/coerce.jl	97.67% <0.00%> (-0.29%)	⬇️
src/convention/coerce.jl	98.66% <0.00%> (-0.29%)	⬇️
src/convention/scitype.jl	96.55% <0.00%> (-0.12%)	⬇️
src/init.jl	100.00% <0.00%> (ø)
src/schema.jl	100.00% <0.00%> (ø)
src/autotype.jl	100.00% <0.00%> (ø)

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