Update CONTRIBUTING.md

Author: JeroenWeener

CONTRIBUTING.md

@@ -33,7 +33,7 @@ We really appreciate contributions via GitHub pull requests. To contribute take
 
  * Make sure you are up to date with the latest code on the master: 
    * `git fetch upstream`
-   * `git checkout upstream/develop -b <name_of_your_branch>`
+   * `git checkout upstream/main -b <name_of_your_branch>`
  * Apply your changes
  * Verify your changes and fix potential warnings/ errors:
    * Check formatting: `dart format .`
@@ -46,4 +46,4 @@ Send us your pull request:
 
  * Go to `https://github.com/BaseflowIT/flutter-google-api-availability` and click the "Compare & pull request" button.
 
- Please make sure you solved all warnings and errors reported by the static code analyses and that you fill in the full pull request template. Failing to do so will result in us asking you to fix it.
+ Please make sure you solved all warnings and errors reported by the static code analyses and that you fill in the full pull request template. Failing to do so will result in us asking you to fix it.