Adjust test config for Emacs 26 release

Replace 26-pretest with 26.1, and don't mark it as an allowed failure
any more.

.travis.yml

@@ -9,14 +9,13 @@ env:
     - EMACS_VERSION=emacs-25.1
     - EMACS_VERSION=emacs-25.2
     - EMACS_VERSION=emacs-25.3
-    - EMACS_VERSION=emacs-26-pretest
+    - EMACS_VERSION=emacs-26.1
     # For some reason emac-git-snapshot hangs forever
     # - EMACS_VERSION=emacs-git-snapshot
     - EMACS_VERSION=remacs-git-snapshot
 
 matrix:
   allow_failures:
-  - env: EMACS_VERSION=emacs-26-pretest
   - env: EMACS_VERSION=remacs-git-snapshot
   - env: EMACS_VERSION=emacs-git-snapshot