fix outdated env var

docs/integrations/browserstack.mdx

@@ -45,20 +45,20 @@ brew tap leancodepl/tools
 brew install mobile-tools
 ```
 
-The `bs_android` script requires the `BROWSERSTACK_CREDS` environment variable
+The `bs_android` script requires the `BS_CREDENTIALS` environment variable
 to be set so it can authenticate with Browserstack:
 
 ```bash
-export YOUR_USERNAME:YOUR_ACCESS_KEY
+export BS_CREDENTIALS="YOUR_USERNAME:YOUR_ACCESS_KEY"
 ```
 
 Get your username and access on [Browserstack's account page][bs_account].
 
 Now reload your shell (e.g. `exec zsh`) and run `bs_android`:
 
 ```
-$ export BROWSERSTACK_PROJECT=AwesomeApp # optional
-$ export BROWSERSTACK_DEVICES="[\"Google Pixel 4-10.0\"]" # optional
+$ export BS_PROJECT=AwesomeApp # optional
+$ export BS_ANDROID_DEVICES="[\"Google Pixel 4-10.0\"]" # optional
 $ bs_android
 • Building apk with entrypoint test_bundle.dart...
 ✓ Completed building apk with entrypoint test_bundle.dart (11.0s)