Step 4/10 : RUN add-apt-repository -y ppa:ondrej/php
 ---> Running in 3ba19cd44fe8
Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python3.5/threading.py", line 914, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.5/threading.py", line 862, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/lib/python3/dist-packages/softwareproperties/SoftwareProperties.py", line 688, in addkey_func
    func(**kwargs)
  File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 386, in add_key
    return apsk.add_ppa_signing_key()
  File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 252, in add_ppa_signing_key
    tmp_keyring, tmp_secret_keyring, signing_key_fingerprint, tmp_keyring_dir):
  File "/usr/lib/python3/dist-packages/softwareproperties/ppa.py", line 181, in _recv_key
    "--recv", signing_key_fingerprint,
  File "/usr/lib/python3.5/subprocess.py", line 247, in call
    with Popen(*popenargs, **kwargs) as p:
  File "/usr/lib/python3.5/subprocess.py", line 676, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.5/subprocess.py", line 1282, in _execute_child
    raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'gpg'