Use toml 0.5

This allows docs.rs to only have one version of toml, not both 0.4 and
0.5. See rust-lang/docs.rs#459 for context.

Author: jyn514

Cargo.toml

@@ -37,7 +37,7 @@ flate2 = "1"
 tar = "0.4.0"
 percent-encoding = "2.1.0"
 walkdir = "2.2"
-toml = "0.4.6"
+toml = "0.5"
 fs2 = "0.4.3"
 remove_dir_all = "0.5.2"
 base64 = "0.10.1"