Update lxml to 3.4.4

docs/shared/requirements.txt

@@ -34,7 +34,7 @@ feedparser==5.1.3
 git+https://github.com/pmitros/pyfs.git@96e1922348bfe6d99201b9512a9ed946c87b7e0b
 GitPython==0.3.2.RC1
 glob2==0.3
-lxml==3.3.6
+lxml==3.4.4
 mako==0.7.3
 Markdown==2.2.1
 mock==1.0.1

requirements/edx-sandbox/post.txt

@@ -6,4 +6,4 @@
 
 # Packages to install in the Python sandbox for secured execution.
 scipy==0.14.0
-lxml==3.3.6
+lxml==3.4.4

requirements/edx/base.txt

@@ -45,7 +45,7 @@ glob2==0.3
 gunicorn==0.17.4
 httpretty==0.8.3
 lazy==1.1
-lxml==3.3.6
+lxml==3.4.4
 mako==0.9.1
 Markdown==2.2.1
 --allow-external meliae