Prefer single-quoted strings

[mariusbutuc]

RuboCop's Style/StringLiterals recommends to:

Prefer single-quoted strings when you don't need string interpolation or special symbols

I understand that the camps are divided around nitpicks like this one, but this minimal and inexpensive change—in both the docs and the generated code—can reduce number of notices a new user would get.

[mariusbutuc]

Or, I could quote @fxn 😄

prefer single quotes, by the beard of the prophet!

[grosser]

I don't really care either way ... but want to throw in this: https://viget.com/extend/just-use-double-quoted-ruby-strings

afaik there is no significant performance benefit ... avoiding a few rubocop warnings for whoever pastes code is nice ... but I've also seen projects use double-quoted style ... so meh :D

[jonleighton]

Personally, I prefer double quotes, because there's no performance benefit to single quotes, and I hate having to convert the quoting style just to be able to use interpolation.

That said, this PR is really about what style we use in the generated code. If the rest of the code generated by Rails uses single quotes (does it?), we should also probably use single quotes for consistency I suppose.

[fxn]

Yes, Rails has that convention (and the reasoning is not performance, I don't know who started that myth).

[rafaelfranca]

👍 for the change in the generated code, but not for spring code. @mariusbutuc could you update your pull request to change only the generated code?

[rafaelfranca]

Looks like everything in this PR is in the generated code. Thanks!