message: changes to mac-build.md
diff: ```
  4. Setup OPENSSL_DIR variable: path to installed openssl library
  ```
  - export OPENSSL_DIR=/usr/local/Cellar/openssl/1.0.2l
  + export OPENSSL_DIR=/usr/local/Cellar/openssl/1.0.2n # path changes with version number
  ```
  5. Checkout and build the library:
  ```
  