bug 1301116: Upgrade setuptools

setuptools 20.7.0 -> 26.1.1: Many fixes

The necessary fix is from 20.8.1:

pypa/setuptools#544

The latest version has been active for a month, which seems like a long
time for setuptools releases.

requirements/constraints.txt

@@ -30,10 +30,10 @@ pytz==2015.7 \
     --hash=sha256:8b6ce1c993909783bc96e0b4f34ea223bff7a4df2c90bdb9c4e0f1ac928689e3
 # cryptography, django-honeypot
 # Force version from Ubuntu 16.04 LTS
-setuptools==20.7.0 \
-    --hash=sha256:8917a52aa3a389893221b173a89dae0471022d32bff3ebc31a1072988aa8039d \
-    --hash=sha256:505cdf282c5f6e3a056e79f0244b8945f3632257bba8469386c6b9b396400233 \
-    --hash=sha256:5704988be46145f68b3b04d599bb03d5b6aaeaf66de8f2896bb1d3ba8aebd7ba
+setuptools==20.8.1 \
+    --hash=sha256:d5bbc1929feeaa81233bdadc0c720d35ac27a3ca7a1f9641f632af822419114d \
+    --hash=sha256:f49be4963e2d985bf12768f46cbfe4b016787f2c0ed1f8f62c3d2bc0362586da \
+    --hash=sha256:7d12cacffaac1b49b26de603b6776f70bf8941461197c47cd3e409ba1e55546c
 # bleach, django-appconf, django-cacheback, django-extensions, mock, etc.
 six==1.10.0 \
     --hash=sha256:0ff78c403d9bccf5a425a6d31a12aa6b47f1c21ca4dc2573a7e2f32a97335eb1 \