[dcl.fct.def.coroutine] Replace \textrm with \text in math mode

Author: jensmaurer

source/declarations.tex

@@ -6447,10 +6447,10 @@
 In the following, $\tcode{p}_i$ is an lvalue of type $\tcode{P}_i$,
 where
 $\tcode{p}_1$ denotes the object parameter and
-$\tcode{p}_{i+1}$ denotes the $i^\textrm{th}$ non-object function parameter
+$\tcode{p}_{i+1}$ denotes the $i^\text{th}$ non-object function parameter
 for a non-static member function, and
 $\tcode{p}_i$ denotes
-the $i^\textrm{th}$ function parameter otherwise.
+the $i^\text{th}$ function parameter otherwise.
 For a non-static member function,
 $\tcode{q}_1$ is an lvalue that denotes \tcode{*this};
 any other $\tcode{q}_i$ is an lvalue