Travis: use homebrew addon instead of doing it manually

This should make our mac builds on Travis faster.

This also switches to the latest xcode / VM image which helps speed things up
(less to update for Homebrew). It turned out that that app directories that we
were creating here didn't run for people, anyway, so why even bother with an
old image.

We still create / upload that image (simply in order to be able to peek into it
in case something goes wrong).

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

.travis.yml

@@ -9,8 +9,22 @@ matrix:
 
     - env: SUBSURFACE_PLATFORM='mac'
       os: osx
-      osx_image: xcode8
-      language: c++ ruby
+      osx_image: xcode10.1
+      language: c++
+      addons:
+        homebrew:
+          packages:
+            - xz
+            - hidapi
+            - libusb
+            - libxml2
+            - libxslt
+            - libzip
+            - openssl
+            - pkg-config
+            - libgit2
+            - libssh2
+          update: true
 
     - env: SUBSURFACE_PLATFORM='windows'
       os: linux

scripts/mac/before_install.sh

@@ -15,16 +15,6 @@ git fetch --unshallow
 git pull --tags
 git describe
 
-# for our build we need an updated Homebrew with a few more components
-# installed.
-#
-# in the past that was brutally slow, but now this is quite fast, so we
-# no longer bother with trying to cache the binaries - the raw download
-# takes longer than updating / installing from Homebrew
-brew update
-echo "Updated Homebrew, now get our dependencies brewed"
-brew install xz hidapi libusb libxml2 libxslt libzip openssl pkg-config libgit2 libssh2
-
 # libdivecomputer uses the wrong include path for libusb and hidapi
 # the pkgconfig file for libusb/hidapi already gives the include path as
 # ../include/libusb-1.0 (../include/hidapi) yet libdivecomputer wants to use