Switch to source serif pro, fix typo in TODO

Letter.tex

@@ -5,14 +5,14 @@
 \usepackage{url}
 \usepackage{xcolor}
 \newcommand{\todo}[1]{\textbf{\textcolor{red}{(TODO: #1)}}}
-\renewcommand{\familydefault}{\sfdefault}
-\usepackage{helvet}
+\usepackage[default,regular,black]{sourceserifpro}
+\usepackage[T1]{fontenc}
 \setkomavar{fromname}{Tim Buchwaldt}
 \setkomavar{fromaddress}{Lukasstr. 16a\\50823 Köln}
 \setkomavar{fromphone}{+49 151 16914796}
 
 \begin{document}
-\begin{letter}{\todo{Add recipient adress}}
+\begin{letter}{\todo{Add recipient address}}
 
 \KOMAoptions{fromphone=true,fromfax=false}
 \setkomavar{subject}{\todo{Add Title}}