CI: build using Racket 6.6 and up, drop Travis CI config (#245)

* ci: run CI for Racket 6.6 and up

Racket 6.5 has an SSL issue that makes it unable to install packages.
That might be why it was not included in the Travis build either.

* ci: drop travis config

.github/workflows/ci.yml

@@ -9,8 +9,23 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        racket-version: ["7.4", "7.5", "7.6", "7.7", "7.8", "7.9", "current"]
+        racket-version: ["6.6", "6.7", "6.8", "6.9", "6.10.1", "6.11", "6.12", "7.0", "7.1", "7.2", "7.3", "7.4", "7.5", "7.6", "7.7", "7.8", "7.9", "current"]
         racket-variant: ["BC", "CS"]
+        # CS builds are only provided for versions 7.4 and up so avoid
+        # running the job for prior versions.
+        exclude:
+          - {racket-version: "6.6",    racket-variant: "CS"}
+          - {racket-version: "6.7",    racket-variant: "CS"}
+          - {racket-version: "6.8",    racket-variant: "CS"}
+          - {racket-version: "6.9",    racket-variant: "CS"}
+          - {racket-version: "6.10.1", racket-variant: "CS"}
+          - {racket-version: "6.11",   racket-variant: "CS"}
+          - {racket-version: "6.12",   racket-variant: "CS"}
+          - {racket-version: "7.0",    racket-variant: "CS"}
+          - {racket-version: "7.1",    racket-variant: "CS"}
+          - {racket-version: "7.2",    racket-variant: "CS"}
+          - {racket-version: "7.3",    racket-variant: "CS"}
+
     steps:
     - name: Checkout
       uses: actions/checkout@master

.travis.yml

@@ -1,46 +0,0 @@
-# adapted from
-# https://github.com/greghendershott/travis-racket/blob/master/.travis.yml
-# Thanks Greg!
-
-dist: trusty
-language: c
-sudo: false
-
-env:
-  global:
-    - RACKET_DIR=~/racket
-  matrix:
-    - RACKET_VERSION=6.3
-    - RACKET_VERSION=6.6
-    - RACKET_VERSION=6.9
-    - RACKET_VERSION=6.12
-    - RACKET_VERSION=7.0
-    - RACKET_VERSION=7.3
-    - RACKET_VERSION=7.4
-    - RACKET_VERSION=7.5
-    - RACKET_VERSION=7.6
-    - RACKET_VERSION=HEAD
-    - RACKET_VERSION=HEADCS
-
-# You may want to test against certain versions of Racket, without
-# having them count against the overall success/failure.
-matrix:
-  allow_failures:
-    - env: RACKET_VERSION=HEAD
-    - env: RACKET_VERSION=HEADCS
-  # Fast finish: Overall build result is determined as soon as any of
-  # its rows have failed, or, all of its rows that aren't allowed to
-  # fail have succeeded.
-  fast_finish: true
-
-before_install:
-  - "export DISPLAY=:99.0" # needed for testing with `racket/gui`
-  - "sh -e /etc/init.d/xvfb start" # needed for testing with `racket/gui`
-  - git clone https://github.com/mbutterick/travis-racket.git
-  - cat travis-racket/install-racket.sh | bash # pipe to bash not sh!
-  - export PATH="${RACKET_DIR}/bin:${PATH}" #install-racket.sh can't set for us
-
-script:
- - cd ..   # Travis did a cd into the dir. Back up, for the next:
- - travis_retry raco pkg install --deps search-auto https://github.com/mbutterick/pollen.git
- - raco test -p pollen