Fix a configuration example in gantt.md

According to the [config schema docs](https://mermaid.js.org/config/schema-docs/config-defs-gantt-diagram-config.html#tickinterval-constraints), Gantt's `tickInterval` configuration must match the following regular expression, which does **not** allow any space:

```regexp
/^([1-9][0-9]*)(millisecond|second|minute|hour|day|week|month)$/
```

packages/mermaid/src/docs/syntax/gantt.md

@@ -390,7 +390,7 @@ mermaid.ganttConfig = {
   sectionFontSize: 24, // Font size for sections
   numberSectionStyles: 1, // The number of alternating section styles
   axisFormat: '%d/%m', // Date/time format of the axis
-  tickInterval: '1 week', // Axis ticks
+  tickInterval: '1week', // Axis ticks
   topAxis: true, // When this flag is set, date labels will be added to the top of the chart
   displayMode: 'compact', // Turns compact mode on
   weekday: 'sunday', // On which day a week-based interval should start