Update to quickcheck 0.8

Fixes #253.
diff --git a/Cargo.toml b/Cargo.toml
index ca207ec..eb700c6 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -27,7 +27,7 @@
 
 [dependencies]
 fixedbitset = { version = "0.1.4" }
-quickcheck = { optional = true, version = "0.7.1", default-features = false }
+quickcheck = { optional = true, version = "0.8", default-features = false }
 indexmap = { version = "1.0.2", optional = true }
 serde = { version = "1.0", optional = true }
 serde_derive = { version = "1.0", optional = true }
diff --git a/serialization-tests/Cargo.toml b/serialization-tests/Cargo.toml
index 063fd44..6ac6e58 100644
--- a/serialization-tests/Cargo.toml
+++ b/serialization-tests/Cargo.toml
@@ -19,6 +19,6 @@
 
 [dev-dependencies]
 serde_json = "1.0"
-quickcheck = { version = "0.7.1", default-features = false }
+quickcheck = { version = "0.8", default-features = false }
 bincode = "1.0.1"
 defmac = "0.1"