python-utils-r1: Default to Python 3.6

Enabling Python 3.8 for SDK packages, but want to keep the default as
3.6 for now.

BUG=b:187794810
TEST=Pass CQ, successful SDK builder tryjob

Change-Id: I2343ae45917f8411e9b6201ffbb10da9a8a7d543
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/eclass-overlay/+/3895296
Tested-by: Sloan Johnson <sloanjohnson@google.com>
Commit-Queue: Sloan Johnson <sloanjohnson@google.com>
Auto-Submit: Sloan Johnson <sloanjohnson@google.com>
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
diff --git a/eclass/python-utils-r1.eclass b/eclass/python-utils-r1.eclass
index 5c8152f..7069100 100644
--- a/eclass/python-utils-r1.eclass
+++ b/eclass/python-utils-r1.eclass
@@ -41,7 +41,7 @@
 _PYTHON_ALL_IMPLS=(
 	pypy3
 	python2_7
-	python3_6 python3_7 python3_8 python3_9
+	python3_7 python3_8 python3_9 python3_6
 )
 readonly _PYTHON_ALL_IMPLS