Update requirements.txt to unpin future and lxml (#252)

* Update requirements.txt to unpin future and lxml
Update lxml to 4.6.2 or newer to resolve vulnerability

* Pin watchdog to <1.0.0 per their docs to maintain Python2.7 compatibility.

Author: Chaffelson

requirements.txt

@@ -3,13 +3,13 @@
 # Basics
 setuptools>=38.5
 six>=1.11.0
-future==0.18.2
+future>=0.18.2
 
 # Version comparison
 packaging>=17.1
 
 # Templates management implementation
-lxml>=4.1.1,<4.4.0  # pyup: ignore
+lxml>=4.6.2
 
 # Security and Connectivity
 requests[security]>=2.18

requirements_dev.txt

@@ -4,7 +4,7 @@ pip>=9.0.1
 
 # Project management and Deployment
 bumpversion>=0.5.3
-watchdog>=0.8.3
+watchdog>=0.8.3,<1.0.0
 twine>=1.9.1,<2.0.0  # pyup: ignore
 virtualenvwrapper>=4.8
 virtualenv>=16.0.0  # required for tox 3.14.2 but not forced