Fix definition of prime in totally ordered group

Thanks to Zhenhua Wu
https://stacks.math.columbia.edu/tag/00IH#comment-8874

Author: aisejohan

Diff for: algebra.tex

@@ -11994,7 +11994,8 @@ \section{Valuation rings}
 An {\it ideal of $\Gamma$} is a subset $I \subset \Gamma$ such
 that all elements of $I$ are $\geq 0$ and $\gamma \in I$,
 $\gamma' \geq \gamma$ implies $\gamma' \in I$. We say that such
-an ideal is {\it prime} if $\gamma + \gamma' \in I, \gamma, \gamma' \geq 0
+an ideal is {\it prime} if $0 \not \in I$ and if
+$\gamma + \gamma' \in I, \gamma, \gamma' \geq 0
 \Rightarrow \gamma \in I \text{ or } \gamma' \in I$.
 
 \begin{lemma}