added 'build' dir to ignore.
added 'build' dir to ignore.

rapidsms/rapidsms-core-dev,caktus/rapidsms,dimagi/rapidsms,eHealthAfrica/rapidsms,ehealthafrica-ci/rapidsms,lsgunth/rapidsms,caktus/rapidsms,caktus/rapidsms,unicefuganda/edtrac,peterayeni/rapidsms,ehealthafrica-ci/rapidsms,unicefuganda/edtrac,rapidsms/rapidsms-core-dev,eHealthAfrica/rapidsms,peterayeni/rapidsms,lsgunth/rapidsms,catalpainternational/rapidsms,eHealthAfrica/rapidsms,ken-muturi/rapidsms,catalpainternational/rapidsms,dimagi/rapidsms,unicefuganda/edtrac,catalpainternational/rapidsms,peterayeni/rapidsms,lsgunth/rapidsms,lsgunth/rapidsms,ken-muturi/rapidsms,ehealthafrica-ci/rapidsms,peterayeni/rapidsms,catalpainternational/rapidsms,ken-muturi/rapidsms