Fix 'last month' link option

Fixes #898

assets/js/dashboard/date.js

@@ -7,8 +7,12 @@ export function formatISO(date) {
 
 export function shiftMonths(date, months) {
   const newDate = new Date(date.getTime())
-  newDate.setMonth(newDate.getMonth() + months)
-  return newDate
+  const d = newDate.getDate();
+  newDate.setMonth(newDate.getMonth() + +months);
+  if (newDate.getDate() != d) {
+    newDate.setDate(0);
+  }
+  return newDate;
 }
 
 export function shiftDays(date, days) {

assets/js/dashboard/datepicker.js

@@ -294,7 +294,7 @@ class DatePicker extends React.Component {
       boldClass = query.period === period ? "font-bold" : "";
     }
 
-    const date = opts.date ? formatISO(opts.date) : false;
+    opts.date = opts.date ? formatISO(opts.date) : false;
 
     const keybinds = {
       'Today': 'D',
@@ -308,7 +308,7 @@ class DatePicker extends React.Component {
 
     return (
       <QueryLink
-        to={{from: false, to: false, date, period, ...opts}}
+        to={{from: false, to: false, period, ...opts}}
         onClick={this.close.bind(this)}
         query={this.props.query}
         className={`${boldClass  } px-4 py-2 md:text-sm leading-tight hover:bg-gray-100

assets/js/dashboard/query.js

@@ -79,8 +79,8 @@ export function navigateToQuery(history, queryFrom, newData) {
 }
 
 class QueryLink extends React.Component {
-  constructor() {
-    super()
+  constructor(props) {
+    super(props)
     this.onClick = this.onClick.bind(this)
   }