Use direct download URLs instead of API

GitHub's API is throttled to 60 requests per hour per IP address when
for non-authenticated calls, which was causing severe CI flakiness.
While this adds another set of URLs to update for each release, the
alternative was adding an OAuth token and maintaining its ownership.
Moreover, this code is simpler than the previous API parsing.

.travis.yml

@@ -15,7 +15,9 @@ addons:
     paths: $(ls powershell*{deb,pkg} | tr "\n" ":")
 
 install:
-  - (cd tools && ./download.sh)
+  - pushd tools
+  - ./download.sh
+  - popd
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then rvm use 2.2.1; fi # Default 2.0.0 Ruby is buggy
 
 script: ./tools/travis.sh

tools/download.sh

@@ -7,10 +7,9 @@ trap '
   kill -s INT "$$"
 ' INT
 
-# Retrieves asset ID and package name of asset ending in argument
-# $info looks like: "id": 1698239, "name": "powershell_0.4.0-1_amd64.deb",
-get_info() {
-    curl -s https://api.github.com/repos/PowerShell/PowerShell/releases/latest | grep -B 1 "name.*$1"
+get_url() {
+    release=v6.0.0-alpha.9
+    echo "https://github.com/PowerShell/PowerShell/releases/download/$release/$1"
 }
 
 # Get OS specific asset ID and package name
@@ -25,7 +24,7 @@ case "$OSTYPE" in
                     sudo yum install -y curl
                 fi
 
-                version=rpm
+                package=powershell-6.0.0_alpha.9-1.el7.centos.x86_64.rpm
                 ;;
             ubuntu)
                 if ! hash curl 2>/dev/null; then
@@ -35,10 +34,10 @@ case "$OSTYPE" in
 
                 case "$VERSION_ID" in
                     14.04)
-                        version=ubuntu1.14.04.1_amd64.deb
+                        package=powershell_6.0.0-alpha.9-1ubuntu1.14.04.1_amd64.deb
                         ;;
                     16.04)
-                        version=ubuntu1.16.04.1_amd64.deb
+                        package=powershell_6.0.0-alpha.9-1ubuntu1.16.04.1_amd64.deb
                         ;;
                     *)
                         echo "Ubuntu $VERSION_ID is not supported!" >&2
@@ -52,7 +51,7 @@ case "$OSTYPE" in
         ;;
     darwin*)
         # We don't check for curl as macOS should have a system version
-        version=pkg
+        package=powershell-6.0.0-alpha.9.pkg
         ;;
     *)
         echo "$OSTYPE is not supported!" >&2
@@ -60,15 +59,7 @@ case "$OSTYPE" in
         ;;
 esac
 
-info=$(get_info "$version")
-
-# Parses $info for asset ID and package name
-read asset package <<< $(echo "$info" | sed 's/[,"]//g' | awk '{ print $2; print $4 }')
-
-# Downloads asset to file
-packageuri=$(curl -s -i -H 'Accept: application/octet-stream' "https://api.github.com/repos/PowerShell/PowerShell/releases/assets/$asset" |
-    grep location | sed 's/location: //g')
-curl -C - -o "$package" ${packageuri%$'\r'}
+curl -L -o "$package" $(get_url "$package")
 
 if [[ ! -r "$package" ]]; then
     echo "ERROR: $package failed to download! Aborting..." >&2