message: Update mac-build.md
  updates paths to openssl and libindy
diff: ```
  4. Setup OPENSSL_DIR variable: path to installed openssl library
  ```
  - export OPENSSL_DIR=/usr/local/Cellar/openssl/1.0.2k
  + export OPENSSL_DIR=/usr/local/Cellar/openssl/1.0.2l
  ```
  5. Checkout and build the library:
  ```
  git clone https://github.com/hyperledger/indy-sdk.git
  - cd ./indy-sdk
  + cd ./indy-sdk/libindy
  cargo build
  ```
  