Drop space around ':'

According to Hans' suggestion.

Co-authored-by: Hans Olsson <HansOlsson@users.noreply.github.com>

chapters/equations.tex

@@ -140,7 +140,7 @@ \subsubsection{Implicit Iteration Ranges of For-Equations}\label{implicit-iterat
 \begin{lstlisting}[language=modelica]
   Real x[n], y[n];
 equation
-  for i loop          // Same as: for i in 1 : size(x, 1) loop
+  for i loop          // Same as: for i in 1:size(x, 1) loop
     x[i] = 2 * y[i];
   end for;
 \end{lstlisting}