Update AppVeyor for Ubuntu 18.04

.appveyor.yml

@@ -1,6 +1,12 @@
+# brian's standard Appveyor config for Perl 5 modules
+# https://github.com/briandfoy/brians_perl_modules_appveyor_config
+# This file is licensed under the Artistic License 2.0
+
 image:
   - Visual Studio 2015
-  - Ubuntu
+  - ubuntu1604
+  - ubuntu1804
+  - ubuntu
 
 environment:
   PERL5LIB: /home/appveyor/perl5/lib/perl5
@@ -17,12 +23,12 @@ skip_tags: true
 install:
   - cmd: if not exist "C:\strawberry" cinst strawberryperl
   - cmd: set PATH=C:\strawberry\perl\bin;C:\strawberry\perl\site\bin;C:\strawberry\c\bin;%PATH%
-  - cmd: cd C:\projects\%APPVEYOR_PROJECT_NAME%
+  - cmd: cd %APPVEYOR_BUILD_FOLDER%
   - sh: sudo apt-get install build-essential git libssl-dev
   - sh: sudo apt-get install -y perl
   - sh: export PATH=/home/appveyor/perl5/bin:$PATH
   - perl -v
-  - cpan App::cpanminus
+  - cpan App::cpanminus ExtUtils::MakeMaker
   - cpanm --installdeps .
 
 build_script: