Revert "Leibniz-Institute -> Leibniz Institue in invoice footer"

This reverts commit 3140f4bcc4c0881facfa87f047dd9dd1ed6d1347.
diff --git a/invoice.php b/invoice.php
index 94b85a8..d51f0e9 100644
--- a/invoice.php
+++ b/invoice.php
@@ -95,7 +95,7 @@
 
     $invoice->addParagraph("Please transfer the total amount due to our account: ");
 
-    $invoice->addParagraph("Leibniz Institute for the German Language
+    $invoice->addParagraph("Leibniz-Institute for the German Language
 IBAN: DE70 6708 0050 0694 9411 00
 BIC: DRESDEFF670
 Commerzbank Mannheim