Fix language-server installation command in CLI docs

Signed-off-by: Faizan Azim <faizanazim11@gmail.com>

Author: faizanazim11

docs/03_reference/cli.md

@@ -49,7 +49,7 @@ pip install robotcode[runner]
 pip install robotcode[analyze]
 pip install robotcode[debugger]
 pip install robotcode[repl]
-pip install robotcode[language-server]
+pip install robotcode[languageserver]
 ```
 
 To install all packages, including optional dependencies, use: