Drop support for Ubuntu 14.04

Ubuntu 14.04 contains old Qt 5.2.1 Recent fixes of Qt deprecation
warnings breaks the build. Fixing this would mean adding additional
`ifdef`s.

Signed-off-by: Lukas Holecek <hluk@email.cz>

CMakeLists.txt

@@ -44,7 +44,7 @@ endif()
 
 set(CMAKE_AUTOMOC ON)
 
-find_package(Qt5Widgets 5.1.0 REQUIRED)
+find_package(Qt5Widgets 5.5.0 REQUIRED)
 list(APPEND copyq_LIBRARIES Qt5::Widgets)
 
 set(copyq_APP_ID      com.github.hluk.copyq)

utils/debian/create_source_packages.sh

@@ -2,7 +2,6 @@
 set -e
 
 distros=(
-    trusty
     xenial
     bionic
     disco