Update assertion

Author: cartermp

integrationtests/Paket.IntegrationTests/PackSpecs.fs

@@ -945,7 +945,7 @@ let ``#3710 specify license expression and icon``() =
     let nuspec = File.ReadAllText(nuspecFile.FullName)
     let expectedLicense = """<license type="expression">MIT</license>"""
     let expectedIcon = """<icon>guy-fieri.jpg</icon>"""
-    let expectedFile = """<file src="guy-fieri.jpg" target="" />"""
+    let expectedFile = """<file src="guy-fieri.jpg" target="img" />"""
     if not (nuspec.Contains expectedLicense) then
         failwith ("nuspec doesn't have the license expression.\n" + nuspec)
     if not (nuspec.Contains expectedIcon) then