add newer emacsen to CI matrix (#131)

Reworked the CI to do what flycheck does these days, it runs emacs in
docker. The old makefile based emacs installation is busted for
emacs26+, emacs26 fails to build gnutls and can't connect to melpa and
the makefile doesn't even consider emacs27.

Author: rski

.travis.yml

@@ -4,27 +4,23 @@ matrix:
   fast_finish: true
   # Allow snapshot to fail
   allow_failures:
-    - env: EMACS_VERSION=snapshot
-cache:
-  - directories:
-      - .cask/
+    - env: EMACS_VERSION="master"
+services:
+  - docker
 env:
   matrix:
-    - EMACS_VERSION=24.4
-    - EMACS_VERSION=24.5
-    - EMACS_VERSION=25.1
-    - EMACS_VERSION=25.2
-    - EMACS_VERSION=snapshot
+    - EMACS_VERSION="25.3"
+    - EMACS_VERSION="26.3"
+    - EMACS_VERSION="27.1"
+    - EMACS_VERSION="master"
 before_install:
-  - export PATH="$HOME/bin:$PATH"
-  - wget 'https://raw.githubusercontent.com/flycheck/emacs-travis/master/emacs-travis.mk'
-  - make -f emacs-travis.mk install_emacs
-  - make -f emacs-travis.mk install_cask
-  - emacs --version
-install:
-  - cask install
+  - docker pull flycheck/emacs-cask:$EMACS_VERSION
 script:
-  - make compile test
+  - |
+    docker run --volume "$TRAVIS_BUILD_DIR":/puppet-mode \
+               --workdir /puppet-mode \
+               flycheck/emacs-cask:$EMACS_VERSION \
+               /bin/bash -c "make compile test"
 notifications:
   email: false
   webhooks: https://voxpupu.li/incoming/travis

Makefile

@@ -24,5 +24,9 @@ test: $(PKGDIR)
 	$(CASK) exec $(EMACS) -Q --batch $(EMACSFLAGS) -f batch-byte-compile $<
 
 $(PKGDIR) : Cask
-	$(CASK) install
+	@# this is a load bearing --verbose
+	@# without it pkg-info fails to install in emacs 25.3 with the error
+	@# Dependency pkg-info failed to install: Wrong type argument: stringp, nil
+	@# Most likely a bug in cask.
+	$(CASK) --verbose install
 	touch $(PKGDIR)