Fix macOS builds in travis-ci

Author: sledgehammer999

.travis.yml

@@ -134,14 +134,20 @@ install:
         cp "version" $HOME/hombebrew_cache
         cd "$HOME/hombebrew_cache"
         wget https://builds.shiki.hu/homebrew/libtorrent-rasterbar.rb
-        wget https://builds.shiki.hu/homebrew/libtorrent-rasterbar--1.1.9+git20180812.0bcf6cef23+patched-configure.el_capitan.bottle.tar.gz
+        wget https://builds.shiki.hu/homebrew/5146d2df7e48f321511273fb9829ebdc3a6dc519f9ef36a344a343ae524c3ae6--libtorrent-rasterbar-1.1.9+git20180812.0bcf6cef23+patched-configure.el_capitan.bottle.tar.gz
       fi
 
-      # Copy custom libtorrent bottle to homebrew's cache so it can find and install it
+      # Copy custom libtorrent bottle to homebrew's download cache so it can find and install it
       # Also install our custom libtorrent formula by passing the local path to it
       # These 2 files are restored from Travis' cache.
-      cp "$HOME/hombebrew_cache/libtorrent-rasterbar--1.1.9+git20180812.0bcf6cef23+patched-configure.el_capitan.bottle.tar.gz" "$(brew --cache)"
+      cp "$HOME/hombebrew_cache/5146d2df7e48f321511273fb9829ebdc3a6dc519f9ef36a344a343ae524c3ae6--libtorrent-rasterbar-1.1.9+git20180812.0bcf6cef23+patched-configure.el_capitan.bottle.tar.gz" "$(brew --cache)/downloads"
       brew install "$HOME/hombebrew_cache/libtorrent-rasterbar.rb"
+      
+      # NOTE about the bottle name
+      # The part before the "--" characters is a sha256 hash of the string
+      # of the URL homebrew itself would use to download the bottle.
+      # In this case the URL is the following:
+      # http://127.0.0.1/libtorrent-rasterbar-1.1.9+git20180812.0bcf6cef23+patched-configure.el_capitan.bottle.tar.gz
 
       if [ "$build_system" = "cmake" ]; then
         brew outdated cmake || brew upgrade cmake