ci(R): Speed up R build on Travis (#110)
ci(R): Speed up R build on Travis (#110)

* ci(R): Use r_binary_packages

* ci(R): Change into r dir

* ci(R): Use Xenial for binary packages

* ci(R): Specify roxygen2

* ci(R): Specify sudo: true

* ci(R): Install lintr from Github

* ci(R): Don't do recursive make

* ci(R): Don't cd in after_success

stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila,stencila/stencila