Auto merge of #13225 - santagada:patch-1, r=larsbergstrom

Update openssl location for osx homebrew

<!-- Please describe your changes on the following line: -->

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [ ] There are tests for these changes OR
- [x] These changes do not require tests because its a documentation change

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

the location of openssl might have changed, but it reads as of now:

```sh
$ brew link --force openssl
Warning: Refusing to link: openssl
Linking keg-only openssl means you may end up linking against the insecure,
deprecated system OpenSSL while using the headers from Homebrew's openssl.
Instead, pass the full include/library paths to your compiler e.g.:
  -I/usr/local/opt/openssl/include -L/usr/local/opt/openssl/lib
```

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/13225)
<!-- Reviewable:end -->

README.md

@@ -49,7 +49,8 @@ Warning: Refusing to link: openssl
 followed by a compile error not being able to find one or more
 openssl/ include files, you may want to try:
 ```sh
-export DEP_OPENSSL_INCLUDE=/usr/local/include
+export OPENSSL_INCLUDE_DIR="$(brew --prefix openssl)/include"
+export OPENSSL_LIB_DIR="$(brew --prefix openssl)/lib"
 ./mach build ...
 ```