Add yasm dependency to travis build
Add yasm dependency to travis build

dbmdz/iiif-image-api,dbmdz/iiif-image-api,dbmdz/iiif-image-api,dbmdz/iiif-image-api,dbmdz/iiif-image-api,dbmdz/iiif-image-api,dbmdz/iiif-image-api