Auto merge of #50 - rphmeier:bump-heapsize, r=jdm

bump heapsize to 0.4.0

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Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "smallvec"
-version = "0.3.3"
+version = "0.4.0"
 authors = ["Simon Sapin <[email protected]>"]
 license = "MPL-2.0"
 repository = "https://github.com/servo/rust-smallvec"
@@ -17,4 +17,4 @@ name = "smallvec"
 path = "lib.rs"
 
 [dependencies]
-heapsize = { version = "0.3", optional = true }
+heapsize = { version = "0.4", optional = true }