Allow to use this gem in a Ractor

[Edouard-chin]

Fix #70

Problem

I'd like to be able to use this gem inside a Ractor. This is currently not possible because all strings in this library aren't frozen.

Ractor.new do
  UserAgent::Browsers::Chrome::ChromeBrowsers
end.join

# <Thread:0x0000000127f1d128 run> terminated with exception (report_on_exception is true):
# 'block in <top (required)>': can not access non-shareable objects in constant UserAgent::Browsers::Chrome::ChromeBrowsers by non-main Ractor. (Ractor::IsolationError)

Solution

There is no codepaths that depend on mutating these strings so the solution is as simple as turning on the frozen_string_literal magic comment.

[Edouard-chin]

@gshutler Sorry to bother and thanks a lot for your work on this gem. Do you by any chance still maintain this gem, and if yes would you mind having a look at this PR which should be straightforward I think.

For context, I discovered this problem in this gem because we are trying to change Rails to be able to serve requests from a Ractor (and Rails uses this gem as traversal dependencies for allowing/denying certain browsers).