fix(docs): fixed plugins docs, fixes grafana#5777

Author: torkelo

docs/sources/plugins/installation.md

@@ -9,7 +9,7 @@ page_keywords: grafana, plugins, documentation
 The easiest way to install plugins is by using the CLI tool grafana-cli which is bundled with grafana. Before any modification take place after modifying plugins, grafana-server needs to be restarted.
 
 ### Grafana plugin directory
-On Linux systems the grafana-cli will assume that the grafana plugin directory is `/var/lib/grafana/plugins`. It's possible to override the directory which grafana-cli will operate on by specifying the --path flag. On Windows systems this parameter have to be specified for every call.
+On Linux systems the grafana-cli will assume that the grafana plugin directory is `/var/lib/grafana/plugins`. It's possible to override the directory which grafana-cli will operate on by specifying the --pluginsDir flag. On Windows systems this parameter have to be specified for every call.
 
 ### Grafana-cli commands