[bootstrap] Set default channel-priority to "strict" due to issues with beta...

[bootstrap] Set default channel-priority to "strict" due to issues with beta builds using mixed stable/beta sources

bob/devtools/bootstrap.py

@@ -17,6 +17,7 @@ ssl_verify: false #!final
 remote_connect_timeout_secs: 120.0 #!final
 remote_max_retries: 50 #!final
 remote_read_timeout_secs: 180.0 #!final
+channel_priority: strict #!final
 channels:
   - defaults
 conda_build: #!final