Import mainargs @main annotation in scripts (#2044)

This fixed compile issues, when compiled outside of Ammonite.

Pull request: #2044

Author: lefou

ci/shared.sc

@@ -5,6 +5,7 @@
  */
 
 import $ivy.`org.scalaj::scalaj-http:2.4.2`
+import mainargs.main
 
 def unpackZip(zipDest: os.Path, url: String) = {
   println(s"Unpacking zip $url into $zipDest")

ci/upload.sc

@@ -1,6 +1,7 @@
 #!/usr/bin/env amm
 
 import scalaj.http._
+import mainargs.main
 
 @main
 def apply(