Update vendored dependencies for pip 20.1

[pradyunsg]

A tracking issue so that I don't forget about it. :)

[pradyunsg]

Hmm... There's quite a bit.

I do think it'd be worthwhile to improve our situation w/ toml + pytoml + pep517. :)

diff --git a/src/pip/_vendor/vendor.txt b/sandbox.ignore/2020-04-vendor-update.txt
index f8743e87..80a15665 100644
--- a/./src/pip/_vendor/vendor.txt
+++ b/tmp/spam.txt
@@ -1,24 +1,25 @@
 appdirs==1.4.3
 CacheControl==0.12.6
 colorama==0.4.3
-contextlib2==0.6.0
+contextlib2==0.6.0.post1
 distlib==0.3.0
-distro==1.4.0
+distro==1.5.0
 html5lib==1.0.1
-ipaddress==1.0.23  # Only needed on 2.6 and 2.7
-msgpack==0.6.2
-packaging==20.1
-pep517==0.7.0
+ipaddress==1.0.23
+msgpack==1.0.0
+packaging==20.3
+pep517==0.8.2
 progress==1.5
-pyparsing==2.4.6
+pyparsing==2.4.7
 pytoml==0.1.21
-requests==2.22.0
-    certifi==2019.11.28
+requests==2.23.0
+    certifi==2020.4.5.1
     chardet==3.0.4
-    idna==2.8
-    urllib3==1.25.7
+    idna==2.9
+    urllib3==1.25.8
 resolvelib==0.3.0
 retrying==1.3.3
-setuptools==44.0.0
+setuptools==46.1.3
 six==1.14.0
+toml==0.10.0
 webencodings==0.5.1