When selecting Squash merge, the commit message gets truncated

Issue Summary

When merging a Pull request and selecting the Squash merge strategy, long commit messages get truncated and users have to manually fix that. It would be great not to truncate the commits. 

Steps to Reproduce

1. Create a new branch 
2. Commit something to this new branch 
3. Add a large commit message to this commit 
4. Create a Pull Request to merge this commit to another branch 
5. The description of the Pull Request will be automatically filled with the large commit message 
6. Click Merge to merge this Pull Request > select Squash merge 
7. The commit message will be automatically filled with the large commit message 

Expected Results

The message is complete

Actual Results

The message gets truncated

Workaround

You can manually change the commit message