Fix for issue #112.

While trying to install PHP 5.5 via a Dockerfile, Fig kept throwing an exception when processing `RUN add-apt-repository ppa:ondrej/php5` (also see #112):

    UnicodeEncodeError: 'ascii' codec can't encode character u'\ufffd' in position 66: ordinal not in range(128)

The maintainer's name of the `ppa:ondrej/php5` package archive is: Ondřej Surý. The special characters - according to [this post](https://rollbar.com/post/6/unicodeencodeerror-ascii-codec-can-t-encode-character-u-ufffd-in-position-108-ordinal-not-in-range-128) - cause the `UnicodeEncodeError`.

By encoding the line the exception isn't throwed anymore, yet the output isn't pretty (especially the 9th line):

	Step 1 : RUN add-apt-repository ppa:ondrej/php5
	 ---> Running in 57afa071dcb6
	Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /tmp/tmp.d0aPiNsLuo --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --p
	rimary-keyring /etc/apt/trusted.gpg --keyserver hkp://keyserver.ubuntu.com:80/ --recv 14AA40EC0831756756D7F66C4F4EA0AAE5267A6C
	gpg:
	requesting key E5267A6C from hkp server keyserver.ubuntu.com

	gpg:
	key E5267A6C: public key "Launchpad PPA for Ond\xc5\x99ej Sur<EF><BF><BD>" imported

	gpg:
	Total number processed: 1

	gpg:
	              imported: 1
	  (RSA: 1)


	You are about to add the following PPA to your system:
	 This branch follows latest PHP packages as maintained by me & rest of the Debian pkg-php team.
	You can get more information about the packages at https://sury.org
	If you need to stay with PHP 5.4 you can use the oldstable PHP repository:
	<C2><A0><C2><A0><C2><A0><C2><A0>ppa:ondrej/php5-oldstable
	PLEASE READ: If you like my work and want to give me a little motivation, please consider donating: https://deb.sury.org/pages/donate.html
	 More info: https://launchpad.net/~ondrej/+archive/php5
	 ---> 463424d0a65d

The PR fixes this breaking bug for now. Any thoughts on how to properly fix this?