Ruby hooks failing with rbenv installed
Pre-commit has been failing for the past few weeks.

https://gist.github.com/ThatGerber/d6533155848076b25e5e0d5cb02e20eb

Seems to be an issue with the ruby (rbenv) environment.

Tried running `pre-commit clean && pre-commit` but it returns the same issue. Setting `rbenv global 2.2.4` and `rbenv shell 2.2.4` does help either.

diff --git a/pre_commit/languages/ruby.py b/pre_commit/languages/ruby.py
index dc320b3..28ad377 100644
--- a/pre_commit/languages/ruby.py
+++ b/pre_commit/languages/ruby.py
@@ -19,16 +19,18 @@ ENVIRONMENT_DIR = 'rbenv'
 
 
 def get_env_patch(venv, language_version):
-    return (
+    patches = (
         ('GEM_HOME', os.path.join(venv, 'gems')),
         ('RBENV_ROOT', venv),
-        ('RBENV_VERSION', language_version),
         ('PATH', (
             os.path.join(venv, 'gems', 'bin'), os.pathsep,
             os.path.join(venv, 'shims'), os.pathsep,
             os.path.join(venv, 'bin'), os.pathsep, Var('PATH'),
         )),
     )
+    if language_version != 'default':
+        patches += (('RBENV_VERSION', language_version),)
+    return patches
 
 
 @contextlib.contextmanager
['pre_commit/languages/ruby.py']