PyUP - Dependency Update Scheduled daily dependency update on saturday (#892)

* Pin nltk to latest version 3.4

* Update requirements_extra.txt

* Update CHANGELOG.md

Author: pyup-bot

CHANGELOG.md

@@ -74,6 +74,7 @@ To release a new version, please update the changelog as followed:
 ### Changed
 
 ### Dependencies Update
+- nltk>=3.3,<3.4 => nltk>=3.3,<3.5 (PR #892)
 - pytest>=3.6,<3.11 => pytest>=3.6,<4.1 (PR #889)
 
 ### Deprecated

requirements/requirements_extra.txt

@@ -1,2 +1,2 @@
 opencv-python>=3.4,<3.5
-nltk>=3.3,<3.4
+nltk>=3.3,<3.5