cel-thesis.cls: fix umlaut

cel-thesis.cls

@@ -37,7 +37,7 @@
 \thesisTitle{Random Thesis Title}
 \thesisType{Master Thesis Type}
 \thesisAuthor{John Doe}
-\thesisAdvisor{Dr.-Ing. Holger Jäkel}
+\thesisAdvisor{Dr.-Ing. Holger J\"akel}
 \thesisHeadOfInstitute{N. N.}
 \thesisSupervisor{Super-Assi Deluxe M.Sc.}
 \thesisStartDate{dd.mm.yyyy}