Use templateSrv to interpolate timeFrom and timeTo variables. (#31)

I realized that `timeFrom` and `timeTo` variables can be used to access the
overridden time range values at the panel level (Query Options). Those
variables were interpolated using a regex instead of using `templateSrv`, thus
preventing custom date formats to be used. With this change, it's now possible
to specify a custom date format for `timeFrom` and `timeTo` variables if
running on Grafana >= v7.2. For example:

```
query {
  data:submissions(
    where: {
      submitTime: {_gte: "${timeFrom:date}", _lte: "${timeTo:date}"},
    }
  ) {
    Time:submitTime
  }
}
```

Author: carvid

dist/module.js

@@ -25,7 +25,7 @@
       { "name": "GitHub Security Advisories", "path": "img/github_security_advisories.png"}
     ],
     "version": "1.1.3",
-    "updated": "2020-08-14"
+    "updated": "2020-10-20"
   },
 
   "dependencies": {

dist/module.js.map

@@ -70,8 +70,10 @@ export class DataSource extends DataSourceApi<MyQuery, MyDataSourceOptions> {
   private createQuery(query: MyQuery, range: TimeRange | undefined, scopedVars: ScopedVars | undefined = undefined) {
     let payload = query.queryText;
     if (range) {
-      payload = payload.replace(/\$timeFrom/g, range.from.valueOf().toString());
-      payload = payload.replace(/\$timeTo/g, range.to.valueOf().toString());
+      payload = getTemplateSrv().replace(payload, {
+        timeFrom: { text: 'from', value: range.from.valueOf() },
+        timeTo: { text: 'to', value: range.to.valueOf() },
+      });
     }
     payload = getTemplateSrv().replace(payload, scopedVars);