docs: fix brew command

kawarimidoll · web-flow · commit 10af3f23a2ec · 2021-01-08T11:21:41.000+09:00
Calling brew cask install is disabled
diff --git a/README.md b/README.md
@@ -21,7 +21,7 @@ Pixel Picker is like Digital Color Meter, but lives in your menu bar and lets yo
 #### Via Homebrew:
 
 ```bash
-brew cask install pixel-picker
+brew install --cask pixel-picker
 ```
 
 #### Via GitHub Releases
