poky.ent: Updated CentOS required package

Replaced "python34-pip" package with "python3-pip"
in the list of required packages for CentOS' variable.

(From yocto-docs rev: 5d48ea7953169b4392d6caf0fb8f2f952479f033)

Signed-off-by: Kristi Rifenbark <kristi.rifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/poky.ent

@@ -77,5 +77,5 @@
      $ sudo yum makecache
      $ sudo yum install gawk make wget tar bzip2 gzip python unzip perl patch \
      diffutils diffstat git cpp gcc gcc-c++ glibc-devel texinfo chrpath socat \
-     perl-Data-Dumper perl-Text-ParseWords perl-Thread-Queue python34-pip xz \
+     perl-Data-Dumper perl-Text-ParseWords perl-Thread-Queue python3-pip xz \
      which">