fix: Amazon-Price-Alert/requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-LXML-2940874

Author: snyk-bot

Amazon-Price-Alert/requirements.txt

@@ -6,7 +6,7 @@ chardet==3.0.4
 cssselect==1.1.0
 fake-useragent==0.1.11
 idna==2.10
-lxml==4.6.5
+lxml==4.9.1
 parse==1.18.0
 pyee==7.0.4
 pyppeteer==0.2.2