fix binder badge (#245)

Author: atravitz

.github/workflows/binder-badge.yaml

@@ -21,7 +21,7 @@ jobs:
             issue_number: context.issue.number,
             owner: context.repo.owner,
             repo: context.repo.repo,
-            body: `[![Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/OpenFreeEnergy/ExampleNotebooks/blob/${PR_HEAD_REF}/showcase)) :point_left: Launch a Colab session on branch ``${PR_HEAD_REF}``.
+            body: `[![Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/OpenFreeEnergy/ExampleNotebooks/blob/${PR_HEAD_REF}/showcase)) :point_left: Launch a Colab session on branch _${PR_HEAD_REF}_`
           })
       env:
         PR_HEAD_REF: ${{ github.event.pull_request.head.ref }}