AppVeyor: replace MSVC 2013 with 2019
diff --git a/.appveyor.yml b/.appveyor.yml
index d86e1d2..453fa12 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -3,17 +3,17 @@
   do_not_increment_build_number: true
 image:
 - Visual Studio 2015
-- Visual Studio 2013
 - Visual Studio 2017
+- Visual Studio 2019
 install:
 - cmd: >-
     set tests=1
 
-    if /i "%APPVEYOR_BUILD_WORKER_IMAGE%"=="Visual Studio 2013" (call "C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" amd64) & (set tests=0)
-
     if /i "%APPVEYOR_BUILD_WORKER_IMAGE%"=="Visual Studio 2015" (call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x86) & (set QTDIR=C:\Qt\5.9\msvc2015)
 
-    if /i "%APPVEYOR_BUILD_WORKER_IMAGE%"=="Visual Studio 2017" (call "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat" x64) & (set QTDIR=C:\Qt\5.9\msvc2017_64)
+    if /i "%APPVEYOR_BUILD_WORKER_IMAGE%"=="Visual Studio 2017" (call "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat" x64) & (set QTDIR=C:\Qt\5.12\msvc2017_64)
+
+    if /i "%APPVEYOR_BUILD_WORKER_IMAGE%"=="Visual Studio 2019" (call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Auxiliary\Build\vcvarsall.bat" x64) & (set QTDIR=C:\Qt\5.15\msvc2019_64)
 
     set path=%PATH%;%QTDIR%\bin
 build_script: