Office365OAuthService: Restore Accept header in user info request

In update of scribe version change: I68717ebb988 Accept header was
inadvertently removed. Restore the setting of Accept header to "*/*":

  request.addHeader("Accept", "*/*");

Bug: Issue davido/gerrit-oauth-provider#144
Change-Id: I224f798c7fb37e24be7f4fecfc29e11932c51286

src/main/java/com/googlesource/gerrit/plugins/oauth/Office365OAuthService.java

@@ -80,6 +80,7 @@ public OAuthUserInfo getUserInfo(OAuthToken token) throws IOException {
     OAuthRequest request = new OAuthRequest(Verb.GET, PROTECTED_RESOURCE_URL);
     OAuth2AccessToken t = new OAuth2AccessToken(token.getToken(), token.getRaw());
     service.signRequest(t, request);
+    request.addHeader("Accept", "*/*");
 
     JsonElement userJson = null;
     try (Response response = service.execute(request)) {