Fix: Correctly load v8-compile-cache

[zertosh]

v8-compile-cache is not loading because fs.existsSync is checking for a file that doesn't exist. fs.existsSync resolves relative to the cwd, not the current module (like require), and v8CompileCachePath's filename is missing .js.

Instead of checking for the existence of v8-compile-cache.js, just try to require it in a try/catch, using a full path. Also switched the require of cli.js to use the same pattern for consistency (plus it's a module resolution micro-optimization).

# before
$ time ./dist/bin/yarn -v
1.10.0-0
./dist/bin/yarn -v  0.28s user 0.06s system 98% cpu 0.344 total

# after
$ time ./dist/bin/yarn -v
1.10.0-0
./dist/bin/yarn -v  0.16s user 0.05s system 97% cpu 0.213 total

[Daniel15]

Looks good to me. Thanks!