Fix Scaladoc warning
@@ -124,7 +124,7 @@ case class AggregateObservable[TResult](private val wrapped: AggregatePublisher[
* For MongoDB 5.0+, the aggregate command accepts a "let" option. This option is a document consisting of zero or more
* fields representing variables that are accessible to the aggregation pipeline. The key is the name of the variable and the value is
* a constant in the aggregate expression language. Each parameter name is then usable to access the value of the corresponding
- * expression with the "$$" syntax within aggregate expression contexts which may require the use of $expr or a pipeline.
+ * expression with the "$$" syntax within aggregate expression contexts which may require the use of '\$expr' or a pipeline.
*
* @param variables the variables
* @return this
