Restrict dash 1 21 0 (#352)

* Add restriction on dash to not use later versions

* Move version to 1.6.5

Co-authored-by: Mark Gibbs <mark@gibbs.consulting>

django_plotly_dash/version.py

@@ -23,4 +23,4 @@ SOFTWARE.
 
 '''
 
-__version__ = "1.6.4"
+__version__ = "1.6.5"

requirements.txt

-dash>=1.11
+dash>=1.11,<1.21.0
 dash-core-components
 dash-html-components
 dash-renderer