.travis.yml: remove duplicate BUILD_SDIST env
.travis.yml: remove duplicate BUILD_SDIST env

Only build sdist on python3.5, no need to rebuild again in 3.6

googlei18n/compreffor,moyogo/compreffor,moyogo/compreffor,googlefonts/compreffor,googlei18n/compreffor,googlei18n/compreffor,moyogo/compreffor,googlefonts/compreffor