fix(ios): openssl linker issues

[gmurayama]

Applications importing libpitaya can fail during the linking phase for iOS build:

Undefined symbols for architecture arm64:
  "_SSL_get_peer_certificate", referenced from:
      _tls__write_to_bio in libpitaya-ios.a[16](tr_uv_tls_aux.c.o)
ld: symbol(s) not found for architecture arm64
clang++: error: linker command failed with exit code 1 (use -v to see invocation)