DOCSP-33235 Add Space on Agg Project Page (#4835)

Author: ianf-mongodb

source/reference/operator/aggregation/project.txt

@@ -67,7 +67,7 @@ The :pipeline:`$project` specifications have the following forms:
        If the expression evaluates to ``$$REMOVE``, the field is
        excluded in the output. For details, see :ref:`remove-var`.
 
-   * - ``<field>:<0 or false>``
+   * - ``<field>: <0 or false>``
 
      - Specifies the exclusion of a field.