Fix failing tests

I had forgotten to bump the version in the integration tests to match
Diesel's new version. Even though the version is a range, Cargo is bad
at unifying those to one that matches, so it was still compiling Diesel
against 0.9

Author: sgrif

diesel_tests/Cargo.toml

@@ -17,7 +17,7 @@ diesel_codegen = { path = "../diesel_codegen" }
 dotenv = "0.8.0"
 quickcheck = { version = "0.3.1", features = ["unstable"] }
 uuid = { version = ">=0.2.0, <0.4.0" }
-serde_json = "0.8"
+serde_json = "0.9"
 
 [features]
 default = []