If you are like me, then you might have some Ruby projects running on different Ruby versions, so you'll need to either upgrade those old projects to Ruby 2.1.10 or deal with these warnings:
/Users/marc/.rbenv/versions/2.1.0/bin/ruby: warning: RUBY_FREE_MIN is obsolete. Use RUBY_GC_HEAP_FREE_SLOTS instead.
/Users/marc/.rbenv/versions/2.1.0/bin/ruby: warning: RUBY_HEAP_MIN_SLOTS is obsolete. Use RUBY_GC_HEAP_INIT_SLOTS instead.
ruby: warning: RUBY_FREE_MIN is obsolete. Use RUBY_GC_HEAP_FREE_SLOTS instead.
ruby: warning: RUBY_HEAP_MIN_SLOTS is obsolete. Use RUBY_GC_HEAP_INIT_SLOTS instead.