Upgraded base OS to Ubuntu 20.04

Author: Clyde Johnston

texer/Dockerfile

@@ -1,7 +1,7 @@
 #
-# Builds the c_cpp/ubuntu-18.04 toolchain container.
+# Builds the c_cpp/ubuntu-20.04 toolchain container.
 #
-FROM ubuntu:18.04
+FROM ubuntu:20.04
 
 VOLUME /repo
 
@@ -17,13 +17,13 @@ ENV LC_ALL=en_US.UTF-8
 RUN apt-get update
 
 # setup locales in the container so Python can default to utf-8.
+RUN apt-get -y install apt-utils
 RUN apt-get -y install locales
 
 # from http://jaredmarkell.com/docker-and-locales/
 RUN locale-gen en_US.UTF-8
 
 RUN apt-get -y install software-properties-common
-RUN apt-get -y install apt-utils
 RUN apt-get -y install texlive-full
 RUN apt-get -y install lyx
 RUN apt-get -y install inkscape