Change Targets date property default to "now"

The original issue is Target's date property should default to "now"#516.
This PR update the documentation after the PR got approved.
Now that the Target's date property default to 'now', we are updating the docs accordingly.

content/en/apps/reference/targets.md

@@ -34,7 +34,7 @@ All targets are defined in the `targets.js` file as an array of objects accordin
 | `appliesToType` | If `appliesTo: 'reports'`, an array of form codes. If `appliesTo: 'contacts'`, an array of contact types. | Filters the contacts or reports for which `appliesIf` will be evaluated. For example, `['person']` or `['clinic', 'health_center']`. For example, `['pregnancy']` or `['P', 'pregnancy']`. | no |
 | `appliesIf` | `function(contact, report)` | If `appliesTo: 'contacts'`, this function is invoked once per contact and `report` is undefined. If `appliesTo: 'reports'`, this function is invoked once per report. Return true to count this document. For `type: 'percent'`, this controls the denominator. | no |
 | `passesIf` | `function(contact, report)` | For `type: 'percent'`, return true to increment the numerator. | yes, if `type: 'percent'`. Forbidden when `groupBy` is defined. |
-| `date` | `'reported'` or `'now'` or `function(contact, report)` | When `'reported'`, the target will count documents with a `reported_date` within the current month. When `'now'`, target includes all documents. A function can be used to indicate when the document should be counted. Default is `'reported'`. | no |
+| `date` | `'reported'` or `'now'` or `function(contact, report)` | When `'reported'`, the target will count documents with a `reported_date` within the current month. When `'now'`, target includes all documents. A function can be used to indicate when the document should be counted. When this property is undefined or the value is null the default is 'now'. | no |
 | `idType` | `'report'` or `'contact'` or `function(contact, report)` | The target's values are incremented once per unique ID. To count individual contacts that have one or more reports that apply, use `'contact'`. Use `'report'` to count all reports, even if there are multiple that apply for a single contact. If you need more than a single count for each applying contact or report then a custom function can be used returning an array with unique IDs — one element for each count. | no |
 | `groupBy` | `function(contact, report)` returning string | Allows for target ids to be aggregated and scored in groups. Not required for most targets. Use with passesIfGroupCount. | no |
 | `passesIfGroupCount` | `object` | The criteria to determine if the target ids within a group should be counted as passing | yes when `groupBy` is defined |