DIV-784: update copy for income and expenses page

edivorce/apps/core/templates/question/06_children_income_expenses.html

@@ -10,7 +10,7 @@
     <h1><small>Step {% step_order step="children" %}:</small>Children - Income & expenses</h1>
 
     <div class="question-well">
-        <h3>How will you and your spouse be calculating your income?</h3>
+        <h3>How will you and your spouse be determining your income?</h3>
         <p>Under the Federal Guidelines, you can do one of the following:</p>
 
         <div class="radio">