Remove centering for floats (#364)

This was a bad idea...:
https://tex.stackexchange.com/questions/2651/should-i-use-center-or-centering-for-figures-and-tables

floatrows not sure how it should work with flowcharts... so we use
centring

I don't want to redefine all floats either as we use them for chapters
title page.

book/basics/how-sourdough-works.tex

@@ -223,12 +223,11 @@ exception, skip ahead to the end of this section on
 page~\pageref{aggressive-yeast}.}
 
 \begin{figure}[!htb]
-\begin{center}
+\centering
   \includegraphics[width=0.8\textwidth]{saccharomyces-cerevisiae-microscope}
   \caption[Brewer's yeast]{Saccharomyces cerevisiae: Brewer's yeast under the
       microscope.}%
   \label{saccharomyces-cerevisiae-microscope}
-\end{center}
 \end{figure}
 
 Yeasts are saprotrophic fungi. This means that they do not produce their own