Centos: Centos 6 doesn't support sphinx properly

Signed-off-by: Robin Getz <[email protected]>

CI/travis/before_install_linux

@@ -17,15 +17,25 @@ handle_centos() {
 	# FIXME: see about adding `libserialport-dev` from EPEL ; maybe libusb-1.0.0-devel...
 	yum -y groupinstall 'Development Tools'
 	yum -y install cmake libxml2-devel libusb1-devel libaio-devel \
-		bzip2 gzip rpm rpm-build redhat-lsb-core python3-pip
+		bzip2 gzip rpm rpm-build redhat-lsb-core
+
+	# CENTOS 6 doesn't include python 3, it's too old.
+	if is_centos_at_least_ver "7" ; then
+		yum -y install python3-pip
+	fi
 
 	if is_centos_at_least_ver "8" ; then
 		# On CentOS 8, avahi-devel & doxygen are in this repo; enable it
 		yum config-manager --set-enabled PowerTools
 	fi
 
-	yum -y install doxygen avahi-devel
-	install_sphinx
+	# CENTOS 6 will has issues with sphinx
+	if is_centos_at_least_ver "7" ; then
+		yum -y install doxygen
+		install_sphinx
+	fi
+
+	yum -y install avahi-devel
 }
 
 handle_centos_docker() {