Use semver-compatible version requirement for serde.

SimonSapin · SimonSapin · commit 7161ea83d52e · 2015-11-18T16:27:59.000+01:00
diff --git a/Cargo.toml b/Cargo.toml
@@ -29,7 +29,7 @@ version = "0.2"
 optional = true
 
 [dependencies.serde]
-version = "*"
+version = "0.6.1"
 optional = true
 
 [dependencies]
