build: bump rusty_racer to ~> 0.1.2

No behavior change (0.1.0 → 0.1.2 is a packaging/build patch bump). Validated on
0.1.2: WPT gate 660/0/15, gem suite 1586/0/35; the prebuilt x86_64-linux gem
installs without a source compile. Lockfile is gitignored, so only the dev
Gemfile constraint moves.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: ursm

Gemfile

@@ -5,7 +5,7 @@ gemspec
 # JS engines: both installed in dev so the spec suite exercises both
 # (CSIM_JS_ENGINE=v8 / =quickjs). Downstream apps add whichever one
 # they want — neither is a hard dependency of the gem itself.
-gem 'rusty_racer', '~> 0.1.0'
+gem 'rusty_racer', '~> 0.1.2'
 gem 'nokogiri'
 gem 'quickjs', '>= 0.18'