docs: fix typos across documentation

[vaibhavmashal]

Description

This PR improves documentation clarity and fixes minor typos across the repository:

1. README.md:

   • Updates deprecated node-uuid package reference to standard uuid in the custom token example.
   • Fixes grammar and typos in documentation:
     • "a requests" -> "requests" (immediate option description)
     • "of it's choosing" -> "of its choosing" (token description)
     • "if exists" -> "if it exists" (:referrer and :url tokens)
     • "Tokens are references by" -> "Tokens are referenced by"
     • "tokens is object" -> "tokens is an object"
     • "log all request" -> "log all requests" (examples header descriptions)

2. index.js:

   • Fixes typo in total-time token comment ("cover to milliseconds" -> "convert to milliseconds").

3. test/morgan.js:

   • Fixes test title typo ("should color 4xx yelow" -> "should color 4xx yellow").

Test plan

• Ran npm test (all 99 tests passing across mocha test suites).
• Ran npm run lint (eslint passing with no errors or warnings).

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[UlisesGascon]

Great Catch!