Remove trailing slash from URL

There's an issue in influxdb crate with that trailing slash.

README.md

@@ -26,7 +26,7 @@ username = "<your username>"
 password = "<your really secret password>"
 
 [influxdb]
-url = "<url to InfluxDB, e.g. http://127.0.0.1:8086/>"
+url = "<url to InfluxDB, e.g. http://127.0.0.1:8086>"
 database = "<your InfluxDB database name>"
 ```