Auto merge of #138 - mbrubeck:bump, r=emilio

Version 0.6.8

Change log:

* Don't leak memory if an iterator panics during `extend` (#137)
* Update the unstable `union` feature for better forward compatibility (#135)

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Author: bors-servo

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "smallvec"
-version = "0.6.7"
+version = "0.6.8"
 authors = ["Simon Sapin <[email protected]>"]
 license = "MIT/Apache-2.0"
 repository = "https://github.com/servo/rust-smallvec"