herokuにアップできなくて困っています。

railsでアプリを作成して、herokuにアップロードしようとしたところエラーが出てしまいました。

gitbashで「git push heroku master」を実行すると下記のエラーが出てしまいます。

今日一日調べましたけど、ぜんぜん解決できそうにないです。

どなたかお分かりになる方、ご教示いただけますでしょうか。

Counting objects: 212, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (192/192), done.
Writing objects: 100% (212/212), 267.13 KiB | 0 bytes/s, done.
Total 212 (delta 34), reused 0 (delta 0)
remote: Compressing source files... done.
remote: Building source:
remote:
remote: ! Warning: Multiple default buildpacks reported the ability to handle this app. The first buildpack in the list below will be used.
remote: Detected buildpacks: Ruby,PHP
remote: See https://devcenter.heroku.com/articles/buildpacks#buildpack-detect-order
remote: -----> Ruby app detected
remote: -----> Compiling Ruby/Rails
remote: -----> Using Ruby version: ruby-2.2.4
remote: -----> Installing dependencies using bundler 1.11.2

中略

remote: Tasks: TOP => assets:precompile
remote: (See full trace by running task with --trace)
remote: !
remote: ! Precompiling assets failed.
remote: !
remote: ! Push rejected, failed to compile Ruby app.
remote:
remote: ! Push failed
remote: Verifying deploy...
remote:
remote: ! Push rejected to enigmatic-savannah-60602.
remote:
To https://git.heroku.com/enigmatic-savannah-60602.git
! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'https://git.heroku.com/enigmatic-savannah-60602.git'