Fix ImportError: cannot import name inputstream

This error was caused by html5lib (itself required by xhtml2pdf).

Ref https://github.com/xhtml2pdf/xhtml2pdf/pull/325
Ref 169a67d

requirements.txt

@@ -11,7 +11,7 @@ django-polymorphic==0.6
 django-sendfile==0.3.6
 django-localflavor==1.1
 -e git+https://code.ffdn.org/zorun/django-postgresql-netfields.git#egg=django-netfields
-xhtml2pdf==0.1b2
+xhtml2pdf==0.1b3
 -e git+https://github.com/jlaine/django-ldapdb@1c4f9f29e52176f4367a1dffec2ecd2e123e2e7a#egg=django-ldapdb
 feedparser
 six==1.10.0