Match the prose order in code voice

[bytedriver]

This PR fixes a tiny text mistake in the sentence that you can find in the section Associated Values of the chapter "Enumerations"

If all of the associated values for an enumeration case are extracted as constants, or if all are extracted as variables, you can place a single var or let annotation before the case name, for brevity:

This PR swaps var and let annotation places in the sentence above.

Fixes #124

[amartini51]

@bytedriver Thanks for making this correction! Do you mind if I reword the commit in terms of what was wrong and why it was changed? Here's my suggested commit message:

Match order in prose and code.

The first part of the sentence lists constants before variables, so put 'let'
before 'var' to match.

[bytedriver]

@amartini51 Thank you for reviewing the changes.
I definitely agree with your suggestion about the commit message.
Please let me know if I have to reset the commit and push a new one with the new message.

[amartini51]

Please let me know if I have to reset the commit and push a new one with the new message.

I made 0f6400a and force-pushed to your branch.

[bytedriver]

@amartini51 Thanks a lot! ❤️