Fix missing semicolon in build.cake

A missing semicolon at the end of a declaration line for 'github_token' variable in the build.cake file was causing a syntax error. This has been fixed by adding the missing semicolon.

build.cake

@@ -3,7 +3,7 @@
 var target = Argument("target", "Default");
 var configuration = Argument("configuration", "Release");
 var nuget_api_key = Argument<string>("nuget_api_key");
-var github_token = Argument<string>("github_token")
+var github_token = Argument<string>("github_token");
 
 string version = String.Empty;
 //////////////////////////////////////////////////////////////////////