Added emacs 26.1 to the test matrix.
Added emacs 26.1 to the test matrix.

emacsmirror/ycmd,abingham/emacs-ycmd,abingham/emacs-ycmd,abingham/emacs-ycmd,abingham/emacs-ycmd,abingham/emacs-ycmd,emacsmirror/ycmd,emacsmirror/ycmd,emacsmirror/ycmd,abingham/emacs-ycmd,emacsmirror/ycmd,emacsmirror/ycmd