Update phf version

Author: vaartis

Cargo.toml

@@ -36,7 +36,7 @@ bufstream = "0.1"
 fallible-iterator = "0.1.3"
 hex = "0.2"
 log = "0.3"
-phf = "=0.7.17"
+phf = "=0.7.18"
 postgres-protocol = "0.1"
 bit-vec = { version = "0.4", optional = true }
 chrono = { version = "0.2.14", optional = true }