fix(datetime): default sizing preserves shape of datetime

[liamdebeasi]

Also see ionic-team/ionic-docs#2087

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

The default sizing of datetime did not look great when placed directly into a page. I also ran into some issues with that when using the datetime in the docs demos I am working on. These updates make the sizing a bit nicer.

next	branch

What is the new behavior?

• Fixed datetime now keeps aspect ratio
• Fixed datetime no longer sets a fixed width, but rather a max width so that the datetime still scales on smaller screens.

Does this introduce a breaking change?

• Yes
• No

Other information

[averyjohnston]

Found a typo, but otherwise this is good to go 👍