Compile using Mono 6.4.0.

.travis.yml

@@ -3,7 +3,7 @@
 
 dist: xenial
 language: csharp
-mono: 5.20.1
+mono: 6.4.0
 
 cache:
   directories:

packaging/linux/buildpackage.sh

@@ -7,7 +7,7 @@ command -v python >/dev/null 2>&1 || { echo >&2 "Linux packaging requires python
 command -v tar >/dev/null 2>&1 || { echo >&2 "Linux packaging requires tar."; exit 1; }
 command -v curl >/dev/null 2>&1 || command -v wget > /dev/null 2>&1 || { echo >&2 "Linux packaging requires curl or wget."; exit 1; }
 
-DEPENDENCIES_TAG="20191003"
+DEPENDENCIES_TAG="20191004"
 
 if [ $# -eq "0" ]; then
 	echo "Usage: $(basename "$0") version [outputdir]"