Fix typo in contributing.md
Fix typo in contributing.md

The test file is named as `test.html` not `tests.html`.

cohuman/canjs,whitecolor/canjs,airhadoken/canjs,thomblake/canjs,rjgotten/canjs,juristr/canjs,rasjani/canjs,rjgotten/canjs,thomblake/canjs,Psykoral/canjs,rasjani/canjs,rjgotten/canjs,UXsree/canjs,whitecolor/canjs,dispatchrabbi/canjs,azazel75/canjs,gsmeets/canjs,bitovi/canjs,patrick-steele-idem/canjs,bitovi/canjs,tracer99/canjs,janza/canjs,yusufsafak/canjs,bitovi/canjs,rasjani/canjs,scorphus/canjs,Psykoral/canjs,thecountofzero/canjs,tracer99/canjs,bitovi/canjs,patrick-steele-idem/canjs,ackl/canjs,cohuman/canjs,beno/canjs,janza/canjs,azazel75/canjs,dispatchrabbi/canjs,asavoy/canjs,cohuman/canjs,UXsree/canjs,thecountofzero/canjs,rjgotten/canjs,gsmeets/canjs,shiftplanning/canjs,Psykoral/canjs,gsmeets/canjs,rasjani/canjs,yusufsafak/canjs,whitecolor/canjs,asavoy/canjs,tracer99/canjs,juristr/canjs,ackl/canjs,patrick-steele-idem/canjs,ackl/canjs,scorphus/canjs,beno/canjs,beno/canjs,Psykoral/canjs,airhadoken/canjs,shiftplanning/canjs