add default outputfile suffixes per https://github.com/pattern-lab/the-spec/issues/26
add default outputfile suffixes per https://github.com/pattern-lab/the-spec/issues/26

KatieMFritz/safs-patternlab-node-gulp-twig,bsmart/pdxr-pl,pattern-lab/edition-node-gulp,pcvonz/pattern_lab_playground,pcvonz/pattern_lab_playground,bsmart/pdxr-pl,pcvonz/pattern_lab_playground,pattern-lab/edition-node-gulp,KatieMFritz/safs-patternlab-node-gulp-twig,patternfly/patternfly-atomic,patternfly/patternfly-atomic