message: Fix appveyor failure, messages differ by platform.
diff: @@ -103,8 +103,10 @@ fn http_auth_offered() {
  ")
  .build();
  + // This is a "contains" check because the last error differs by platform,
  + // may span multiple lines, and isn't relevant to this test.
  assert_that(p.cargo("build"),
  - execs().with_status(101).with_stderr(&format!("\
  + execs().with_status(101).with_stderr_contains(&format!("\
  [UPDATING] git repository `http://{addr}/foo/bar`
  [ERROR] failed to load source for a dependency on `bar`
  @@ -119,8 +121,6 @@ Caused by:
  attempted to find username/password via `credential.helper`, but [..]
  Caused by:
  - curl error: Failed to connect to 127.0.0.1 port [..]: Connection refused
  -; class=Net (12)
  ",
  addr = addr)));
  