feat(build): use es2015 module compile target
feat(build): use es2015 module compile target

fixes #1538

macroorganizm/ng2-bootstrap,felixkubli/ng2-bootstrap,buchslava/angular2-bootstrap,valor-software/ngx-bootstrap,valor-software/ng2-bootstrap,buchslava/angular2-bootstrap,Le0Michine/ng2-bootstrap,felixkubli/ng2-bootstrap,IlyaSurmay/ngx-bootstrap-versioning,Le0Michine/ng2-bootstrap,valor-software/ngx-bootstrap,buchslava/angular2-bootstrap,macroorganizm/ng2-bootstrap,macroorganizm/ng2-bootstrap,valor-software/ngx-bootstrap,erodriguezh/ngx-bootstrap,valor-software/ng2-bootstrap,IlyaSurmay/ngx-bootstrap-versioning,felixkubli/ng2-bootstrap,valor-software/ngx-bootstrap