Center TikZ figures

Because it looks better

book/sourdough-starter/sourdough-starter.tex

@@ -127,9 +127,11 @@ inverted one on top. The container shouldn't be airtight,
 you still want some gas exchange to be possible.
 
 \begin{figure}[!htb]
+\begin{center}
   \input{figures/fig-starter-process.tex}
   \caption{The process of making a sourdough starter from scratch.}%
   \label{fig:sourdough-starter-process}
+\end{center}
 \end{figure}
 
 Now an epic battle begins. In one study scientists
@@ -248,11 +250,13 @@ yeast has been isolated like this from century old sourdough
 starters.
 
 \begin{figure}[!htb]
+\begin{center}
   \input{figures/fig-starter-readiness.tex}
   \caption{A flow chart showing you how to determine if your sourdough starter is ready to be used.
   For checking readiness look at a size increase and take note of your starter's smell. Both are important
   indicators to check for readiness.}%
   \label{fig:sourdough-starter-readiness}
+\end{center}
 \end{figure}
 
 The key signs to look at are bubbles that you see in your starter
@@ -315,6 +319,7 @@ yeast part of your sourdough and balance the fermentation.
 \section{Maintenance}
 
 \begin{figure}[!htb]
+\begin{center}
   \input{figures/fig-starter-maintenance.tex}
   \caption{A full flowchart showing you how to conduct proper sourdough starter maintenance. You can use a
   piece of your dough as the next starter. You can also use left-over starter and feed it again. Choose an
@@ -322,6 +327,7 @@ yeast part of your sourdough and balance the fermentation.
   hydration level. Adjust the water content accordingly when you use a stiff
 starter.}%
   \label{fig:sourdough-maintenance-process}
+\end{center}
 \end{figure}
 
 You have made your sourdough starter and your first bread. How do you perform