Foo compilation error

gistfile1.txt

-----> Cleaning up...
-----> Building foo from herokuish...
-----> Adding BUILD_ENV to build environment...
-----> Fetching custom buildpack
-----> elixir app detected
-----> Checking Erlang and Elixir versions
       Will use the following versions:
       * Stack cedar-14
       * Erlang 18.2.1
       * Elixir 1.2.1
       Will export the following config vars:
       * Config vars DATABASE_URL
       * MIX_ENV=prod
-----> Using cached Erlang 18.2.1
-----> Installing Erlang 18.2.1
       
-----> Using cached Elixir v1.2.1
-----> Installing Elixir v1.2.1
-----> Installing Hex
       * creating /app/.mix/archives/hex-0.11.3.ez
-----> Installing rebar
       * creating /app/.mix/rebar
       * creating /app/.mix/rebar3
-----> Fetching app dependencies with mix
       * Updating g_cloud_storage (https://github.com/aesedepece/g_cloud_storage.git)
       * Updating mongodb (https://github.com/aesedepece/mongodb-erlang.git)
       * Updating bson (git://github.com/comtihon/bson-erlang)
       * Updating pbkdf2 (git://github.com/comtihon/erlang-pbkdf2)
       * Updating poolboy (git://github.com/devinus/poolboy)
       * Updating elixir-pipes (https://github.com/batate/elixir-pipes.git)
       * Updating json_web_token (https://github.com/garyf/json_web_token_ex.git)
       Running dependency resolution
       Dependency resolution completed
       base58: 0.1.0
       certifi: 0.4.0
       cowboy: 1.0.4
       cowlib: 1.0.2
       erlcloud: 0.12.0
       hackney: 1.5.4
       httpoison: 0.8.2
       idna: 1.2.0
       insight: 0.1.3
       jsx: 2.7.2
       lhttpc: 1.3.0
       meck: 0.8.3
       metrics: 1.0.1
       mimerl: 1.0.2
       poison: 1.5.2
       ranch: 1.2.1
       ssl_verify_hostname: 1.0.6
       * Updating httpoison (Hex package)
       Checking package (http://s3.hex.pm.global.prod.fastly.net/tarballs/httpoison-0.8.2.tar)
       Fetched package
       * Updating hackney (Hex package)
       Checking package (http://s3.hex.pm.global.prod.fastly.net/tarballs/hackney-1.5.4.tar)
       * Updating ssl_verify_hostname (Hex package)
       Checking package (http://s3.hex.pm.global.prod.fastly.net/tarballs/ssl_verify_hostname-1.0.6.tar)
       Fetched package
       * Getting metrics (Hex package)
       Checking package (http://s3.hex.pm.global.prod.fastly.net/tarballs/metrics-1.0.1.tar)
       Fetched package
       * Updating idna (Hex package)
       Checking package (http://s3.hex.pm.global.prod.fastly.net/tarballs/idna-1.2.0.tar)
       Fetched package
       * Updating certifi (Hex package)
       Checking package (http://s3.hex.pm.global.prod.fastly.net/tarballs/certifi-0.4.0.tar)
       Fetched package
-----> Copying hex from /app/.mix/archives/hex-0.11.3.ez
-----> Compiling
==> poolboy (compile)
==> idna (compile)
       Compiled src/idna_ucs.erl
       Compiled src/idna_unicode.erl
       Compiled src/idna.erl
       Compiled src/idna_unicode_data2.erl
       Compiled src/punycode.erl
       Compiled src/idna_unicode_data1.erl
==> ssl_verify_hostname
       rebar get-deps compile
       make: rebar: Command not found
       make: *** [erl] Error 127
==> foo
remote: ** (Mix) Could not compile dependency :ssl_verify_hostname, "make" command failed. You can recompile this dependency with "mix deps.compile ssl_verify_hostname", update it with "mix deps.update ssl_verify_hostname" or clean it with "mix deps.clean ssl_verify_hostname"
 ! [remote rejected] elixir -> master (pre-receive hook declined)