fix version of icalendar during install to major version

[niccokunzmann]

See #630 (comment)

This prevents us to wonder about the next major version change and if people get confused.

[coveralls]

Pull Request Test Coverage Report for Build 9661444419

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.652%

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Totals
Change from base Build 9660364734:	0.0%
Covered Lines:	3036
Relevant Lines:	3109

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9661488521

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.652%

---

Totals
Change from base Build 9660364734:	0.0%
Covered Lines:	3036
Relevant Lines:	3109

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💛 - Coveralls

[stevepiercy]

When you release 6.x, this will not be necessary, as pip install will install the latest stable release. Changing it now is premature and harmful.

[niccokunzmann]

When you release 6.x, this will not be necessary, as pip install will install the latest stable release.

It will be useful after the 6.0.0 release so that we can upgrade to version 7 with people being conscious about the version they fix to.

Changing it now is premature and harmful.

I agree, let's wait until a 6.* release is made that is not alpha.