webpack: Use cacheLoader for JS files.
webpack: Use cacheLoader for JS files.

This seems to save over 50% of the webpack startup time in run-dev.py.

showell/zulip,rht/zulip,synicalsyntax/zulip,synicalsyntax/zulip,brainwane/zulip,shubhamdhama/zulip,synicalsyntax/zulip,showell/zulip,showell/zulip,shubhamdhama/zulip,showell/zulip,eeshangarg/zulip,andersk/zulip,zulip/zulip,zulip/zulip,eeshangarg/zulip,rht/zulip,brainwane/zulip,rht/zulip,zulip/zulip,brainwane/zulip,shubhamdhama/zulip,hackerkid/zulip,timabbott/zulip,hackerkid/zulip,brainwane/zulip,punchagan/zulip,showell/zulip,brainwane/zulip,kou/zulip,zulip/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,timabbott/zulip,zulip/zulip,eeshangarg/zulip,punchagan/zulip,timabbott/zulip,kou/zulip,timabbott/zulip,shubhamdhama/zulip,zulip/zulip,hackerkid/zulip,andersk/zulip,rht/zulip,punchagan/zulip,kou/zulip,punchagan/zulip,hackerkid/zulip,andersk/zulip,timabbott/zulip,andersk/zulip,showell/zulip,zulip/zulip,eeshangarg/zulip,eeshangarg/zulip,synicalsyntax/zulip,rht/zulip,timabbott/zulip,shubhamdhama/zulip,kou/zulip,synicalsyntax/zulip,hackerkid/zulip,shubhamdhama/zulip,brainwane/zulip,rht/zulip,rht/zulip,andersk/zulip,shubhamdhama/zulip,eeshangarg/zulip,kou/zulip,eeshangarg/zulip,brainwane/zulip,hackerkid/zulip,punchagan/zulip,showell/zulip,timabbott/zulip,punchagan/zulip,kou/zulip,synicalsyntax/zulip,kou/zulip,synicalsyntax/zulip,andersk/zulip