use the gist gem instead of the gist crate

hopefully this will work on osx and will make everything more
uniform (appveyor is already using the gem instead of the crate)

closes #51

library/compiler-builtins/.travis.yml

@@ -1,5 +1,5 @@
 dist: trusty
-language: generic
+language: ruby
 services: docker
 sudo: required
 

library/compiler-builtins/ci/install.sh

@@ -3,13 +3,15 @@ set -ex
 . $(dirname $0)/env.sh
 
 install_qemu() {
-    case $TRAVIS_OS_NAME in
-        linux)
-            apt-get update
-            apt-get install -y --no-install-recommends \
-                    binfmt-support qemu-user-static
-            ;;
-    esac
+    if [[ $TRAVIS_OS_NAME = "linux" ]]; then
+        apt-get update
+        apt-get install -y --no-install-recommends \
+                binfmt-support qemu-user-static
+    fi
+}
+
+install_gist() {
+    gem install gist
 }
 
 install_binutils() {
@@ -45,6 +47,7 @@ install_xargo() {
 main() {
     if [[ $TRAVIS_OS_NAME == "osx" || ${IN_DOCKER_CONTAINER:-n} == "y" ]]; then
         install_qemu
+        install_gist
         install_binutils
         install_rust
         add_rustup_target

library/compiler-builtins/ci/script.sh

@@ -3,7 +3,7 @@ set -ex
 . $(dirname $0)/env.sh
 
 gist_it() {
-    gist -ap -f "'$1' from commit '$TRAVIS_COMMIT' on branch '$TRAVIS_BRANCH'"
+    gist -d "'$TARGET/rustc-builtins.rlib' from commit '$TRAVIS_COMMIT' on branch '$TRAVIS_BRANCH'"
     echo "Disassembly available at the above URL."
 }
 
@@ -16,14 +16,7 @@ inspect() {
     $PREFIX$NM -g --defined-only target/**/debug/*.rlib
 
     set +e
-    case $TRAVIS_OS_NAME in
-        linux)
-            $PREFIX$OBJDUMP -Cd target/**/release/*.rlib | gist_it "$TARGET/rustc-builtins.rlib"
-            ;;
-        osx)
-            $PREFIX$OBJDUMP -Cd target/**/release/*.rlib
-            ;;
-    esac
+    $PREFIX$OBJDUMP -Cd target/**/release/*.rlib | gist_it
     set -e
 
     # Check presence of weak symbols
@@ -49,7 +42,7 @@ run_tests() {
 
 main() {
     if [[ $TRAVIS_OS_NAME == "linux" && ${IN_DOCKER_CONTAINER:-n} == "n" ]]; then
-        local tag=2016-08-22
+        local tag=2016-08-13
 
         docker run \
                --privileged \