Docker: update base image to ubuntu:20.04 [ci skip] (OSGeo#3043)

Dockerfile

@@ -1,18 +1,18 @@
 ##
 # OSGeo/PROJ
 
-FROM ubuntu:18.04 as builder
+FROM ubuntu:20.04 as builder
 
 MAINTAINER Howard Butler <[email protected]>
 
 ARG DESTDIR="/build"
 
 # Setup build env
 RUN apt-get update -y \
-    && apt-get install -y --fix-missing --no-install-recommends \
+    && DEBIAN_FRONTEND=noninteractive apt-get install -y --fix-missing --no-install-recommends \
             software-properties-common build-essential ca-certificates \
-            make cmake wget unzip libtool automake \
-            zlib1g-dev libsqlite3-dev pkg-config sqlite3 libcurl4-gnutls-dev \
+            cmake wget unzip \
+            zlib1g-dev libsqlite3-dev sqlite3 libcurl4-gnutls-dev \
             libtiff5-dev
 
 COPY . /PROJ
@@ -27,7 +27,7 @@ RUN cd /PROJ \
 
 
 
-FROM ubuntu:18.04 as runner
+FROM ubuntu:20.04 as runner
 
 RUN date
 

docs/docbuild/Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:18.04
+FROM ubuntu:20.04
 
 RUN apt-get -y update && DEBIAN_FRONTEND=noninteractive apt-get install -y \
     python3-dev python3-pip g++ doxygen dvipng latexmk \