Update appveyor to take into account now available packages.

appveyor.yml

@@ -1,26 +1,19 @@
-os: Visual Studio 2013
+os: Visual Studio 2015
 
 environment:
   CMAKE_ARGS: -DCMAKE_BUILD_TYPE=Release
-  NSIS_ROOT: C:\nsis
-  SSL_VER: 1_0_2k
 
 configuration:
   - Release
 
 install:
-  - appveyor DownloadFile http://slproweb.com/download/Win32OpenSSL-%SSL_VER%.exe
-  - Win32OpenSSL-%SSL_VER%.exe /silent /verysilent /sp- /suppressmsgboxes
-  - appveyor DownloadFile ftp://sourceware.org/pub/pthreads-win32/pthreads-w32-2-9-1-release.zip
-  - 7z -y x pthreads-w32-2-9-1-release.zip -oC:\pthreads\
-  - cinst -y nsis
 
 build:
 
 build_script:
   - md build
   - cd build
-  - cmake -DCMAKE_BUILD_TYPE=Release ..
+  - cmake -DCMAKE_BUILD_TYPE=Release -DWITH_THREADING=no ..
   - cmake --build . --config Release
   - cd ..
 
@@ -38,8 +31,3 @@ artifacts:
   #- path: build\client\Release\mosquitto_pub.exe
   #- path: build\client\Release\mosquitto_sub.exe
   #- path: build\src\Release\mosquitto.exe
-
-cache:
-  - C:\OpenSSL-Win32
-  - C:\pthreads
-