Adding Cargo for zuk.

I may want to have it check normal places by default. I haven't done
this as I can see this being used for malicious overwriting of commands.

zsh/environment/host/wok/zshenv

@@ -1,6 +1,9 @@
 export GOPATH="${HOME}/.go"
 export PSQLAPP="/Applications/Postgres.app/Contents/Versions/latest/bin"
+cargo="${HOME}/.cargo/bin:$PATH"
+
 path=(
+    $cargo
     $GOPATH
     $PSQLAPP
     $path)