(GH-141) Update default target

Cake.Recipe is no longer coupled directly to AppVeyor, and instead a more
generic ContinuousIntegration target is the default.

Author: gep13

.appveyor.yml

@@ -7,7 +7,7 @@ image: Visual Studio 2019
 #  Build Script                   #
 #---------------------------------#
 build_script:
-  - ps: .\build.ps1 -Target AppVeyor
+  - ps: .\build.ps1 -Target ContinuousIntegration
 
 # Tests
 test: off