Fix URL pattern for account mails

String placeholders were numbered incorrectly.

Fixes #47.

src/main/java/de/thm/arsnova/service/UserServiceImpl.java

@@ -462,7 +462,7 @@ public class UserServiceImpl extends DefaultEntityServiceImpl<UserProfile> imple
 	private void sendActivationEmail(final UserProfile userProfile) {
 		final String activationKey = userProfile.getAccount().getActivationKey();
 		final String activationUrl = MessageFormat.format(
-				"{0}{1}/login?action=activate&username={3}&key={4}",
+				"{0}{1}/login?action=activate&username={2}&key={3}",
 				rootUrl,
 				customizationPath,
 				UriUtils.encodeQueryParam(userProfile.getLoginId(), "UTF-8"),
@@ -570,7 +570,7 @@ public class UserServiceImpl extends DefaultEntityServiceImpl<UserProfile> imple
 		}
 
 		final String resetPasswordUrl = MessageFormat.format(
-				"{0}{1}/login?action=resetpassword&username={3}&key={4}",
+				"{0}{1}/login?action=resetpassword&username={2}&key={3}",
 				rootUrl,
 				customizationPath,
 				UriUtils.encodeQueryParam(userProfile.getLoginId(), "UTF-8"), account.getPasswordResetKey());