Use /var/lib/mediaproxy-ng as a home directory

Using /use/share/doc/something isn't a good choice since the entire directory
/usr/share/doc could be empty due to system settings.

Signed-off-by: Peter Lemenkov <lemenkov@gmail.com>

el/mediaproxy-ng.spec

@@ -109,7 +109,7 @@ rm -rf %{buildroot}
 %pre
 /usr/sbin/groupadd -r mediaproxy-ng 2> /dev/null || :
 /usr/sbin/useradd -r -g mediaproxy-ng -s /sbin/nologin -c "mediaproxy-ng daemon" \
-	-d %{_docdir}/%{name}-%{version}-%{release} mediaproxy-ng \
+	-d %{_sharedstatedir}/mediaproxy-ng mediaproxy-ng \
 	2> /dev/null || :