Fix it's/its, see description. (#1267)

Per [Cambridge Dictionary](https://dictionary.cambridge.org/grammar/british-grammar/it-s-or-its), `it's` is reserved for `it is` or `it has`, but in this context it is being used as neither of those.

packages/jimp/README.md

@@ -131,7 +131,7 @@ Jimp.read({
   });
 ```
 
-Jimp uses [phin](https://github.com/ethanent/phin) as it's HTTP client. Phin uses [`http.request(options[, callback])`](https://nodejs.org/dist/latest-v8.x/docs/api/http.html#http_http_request_options_callback) or [`https.request(options[, callback])`](https://nodejs.org/dist/latest-v8.x/docs/api/https.html#https_https_request_options_callback) methods for making HTTP requests. Phin parses a `url` with the `url.parse(...)` method and passes it with all the other parameters as an `options` to the [`http.request(options[, callback])`](https://nodejs.org/dist/latest-v8.x/docs/api/http.html#http_http_request_options_callback) or [`https.request(options[, callback])`](https://nodejs.org/dist/latest-v8.x/docs/api/https.html#https_https_request_options_callback) methods.
+Jimp uses [phin](https://github.com/ethanent/phin) as its HTTP client. Phin uses [`http.request(options[, callback])`](https://nodejs.org/dist/latest-v8.x/docs/api/http.html#http_http_request_options_callback) or [`https.request(options[, callback])`](https://nodejs.org/dist/latest-v8.x/docs/api/https.html#https_https_request_options_callback) methods for making HTTP requests. Phin parses a `url` with the `url.parse(...)` method and passes it with all the other parameters as an `options` to the [`http.request(options[, callback])`](https://nodejs.org/dist/latest-v8.x/docs/api/http.html#http_http_request_options_callback) or [`https.request(options[, callback])`](https://nodejs.org/dist/latest-v8.x/docs/api/https.html#https_https_request_options_callback) methods.
 
 Briefly speaking, you can pass any options from [`http.request(options[, callback])`](https://nodejs.org/dist/latest-v8.x/docs/api/http.html#http_http_request_options_callback), [`https.request(options[, callback])`](https://nodejs.org/dist/latest-v8.x/docs/api/https.html#https_https_request_options_callback) or even [`tls.connect(options[, callback])`](https://nodejs.org/dist/latest-v8.x/docs/api/tls.html#tls_tls_connect_options_callback).