Add travis emacs version 26.2 and 26.3

Author: taku0

.travis.yml

@@ -7,7 +7,9 @@ env:
   - EVM_EMACS=emacs-25.1-travis
   - EVM_EMACS=emacs-25.2-travis
   - EVM_EMACS=emacs-25.3-travis
-  - EVM_EMACS=emacs-26.1-travis
+  - EVM_EMACS=emacs-26.1-travis-linux-xenial
+  - EVM_EMACS=emacs-26.2-travis-linux-xenial
+  - EVM_EMACS=emacs-26.3-travis-linux-xenial
 
 before_install:
   - curl -fsSkL https://raw.github.com/rejeep/evm/master/go | bash