Auto merge of #4137 - tshepang:immutable, r=alexcrichton
authorbors <bors@rust-lang.org>
Wed, 7 Jun 2017 17:31:32 +0000 (17:31 +0000)
committerbors <bors@rust-lang.org>
Wed, 7 Jun 2017 17:31:32 +0000 (17:31 +0000)
binding does not need to be mutable


Trivial merge