update dev install command

Author: DenisaCG

binder/postBuild

@@ -32,7 +32,7 @@ _(sys.executable, "-m", "pip", "check")
 # install the labextension
 _("jlpm", "install")
 _("jlpm", "build")
-_(sys.executable, "-m", "pip", "install", "-e", ".")
+_(sys.executable, "-m", "pip", "install", "-e", ".[dev]")
 _(sys.executable, "-m", "jupyter", "labextension", "develop", "--overwrite", ".")
 
 # verify the environment the extension didn't break anything