fix index statement for matrix_operation reverse

Author: mitzimorris

src/functions-reference/matrix_operations.Rmd

@@ -1621,7 +1621,7 @@ Number of components of v less than v[s]
 Return a new vector containing the elements of the argument in reverse order.
 
 <!-- row_vector; reverse; (row_vector v); -->
-\index{{\tt \bfseries reverse }!{\tt (row_vector v): row_vector}|hyperpage}
+\index{{\tt \bfseries reverse }!{\tt (row\_vector v): row\_vector}|hyperpage}
 
 `row_vector` **`reverse`**`(row_vector v)`<br>\newline
 Return a new row vector containing the elements of the argument in reverse order.