Merge pull request #277 from Ensembl/bugfix/pr_template

[ENSCORESW-2820] Update links in pull request template

PULL_REQUEST_TEMPLATE.md

 ## Requirements
 
 - Filling out the template is required. Any pull request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion;
-- Review the [contributing guidelines](https://github.com/Ensembl/ensembl/blob/release/90/CONTRIBUTING.md#why-could-my-pull-request-be-rejected) for this repository; remember in particular:
+- Review the [contributing guidelines](https://github.com/Ensembl/ensembl/blob/master/CONTRIBUTING.md#why-could-my-pull-request-be-rejected) for this repository; remember in particular:
     - do not modify code without testing for regression
     - provide simple unit tests to test the changes
-    - if you change the schema you must patch the test databases as well, see [Updating the schema](https://github.com/Ensembl/ensembl/blob/release/90/CONTRIBUTING.md#updating-the-schema)
+    - if you change the schema you must patch the test databases as well, see [Updating the schema](https://github.com/Ensembl/ensembl/blob/master/CONTRIBUTING.md#updating-the-schema)
     - the PR must not fail unit testing
 
 ## Description