typo in Dockerfile

Dockerfile

@@ -75,7 +75,7 @@ RUN pip install pystan==2.19.1.1 \
  && pip install prophet
 
 # Resolving various dependency issues
-RUN pip install holidays=='<0.18,>=0.17.2'
+RUN pip install 'holidays<0.18,>=0.17.2'
 
 # Switching back to using the `superset` user
 USER superset