servo: Merge #13815 - README: OpenSSL steps on macOS are for 10.11+ (from kivikakk:patch-1); r=jdm

I ignored these instructions because it said `<=`, but this should be the other way around! 🙇‍♀️

---

- (n/a) `./mach build -d` does not report any errors
- (n/a) `./mach test-tidy` does not report any errors

<!-- I'm literally the one fixing GitHub's Markdown parser so this comment won't be necessary to divide the two lists. Soon! -->

- [ ] There are tests for these changes
- [x] These changes do not require tests because they're only to `README.md`

Source-Repo: https://github.com/servo/servo
Source-Revision: f4ed2c6875e4f766b4de93263a25431424215f73

servo/README.md

@@ -37,7 +37,7 @@ pip install virtualenv
 ``` sh
 sudo port install python27 py27-virtualenv cmake
 ```
-#### On OS X <= 10.11 (El Capitan), you also have to install openssl
+#### On OS X >= 10.11 (El Capitan), you also have to install OpenSSL
 
 ``` sh
 brew install openssl
@@ -48,7 +48,7 @@ export OPENSSL_LIB_DIR="$(brew --prefix openssl)/lib"
 ./mach build ...
 ```
 
-If you've already partially compiled servo but forgot to do this step, run ./mach clean, set the shell variables, and recompile.
+If you've already partially compiled servo but forgot to do this step, run `./mach clean`, set the shell variables, and recompile.
 
 #### On Debian-based Linuxes