refactor: Use named constant for clarity

Author: ptbrowne

src/ducks/recurrence/service.js

@@ -13,12 +13,16 @@ import { getLabel } from './utils'
 import addDays from 'date-fns/add_days'
 
 const NB_MONTH_LOOKBACK = 3
+const DAYS_IN_MONTH = 30.5
 
 const makeQueryForTransactions = recurrences => {
   if (recurrences.length === 0) {
     return Q(TRANSACTION_DOCTYPE)
   } else {
-    const lookbackDateLimit = addDays(new Date(), -NB_MONTH_LOOKBACK * 30.5)
+    const lookbackDateLimit = addDays(
+      new Date(),
+      -NB_MONTH_LOOKBACK * DAYS_IN_MONTH
+    )
     const query = Q(TRANSACTION_DOCTYPE).where({
       date: {
         $gt: lookbackDateLimit.toISOString().slice(0, 10)