Update VE core submodule to master (e64d6e7)

New changes:
c0fa88a Cleanup SpecialCharacterInspector
50fe498 Store previous range in breakpoint for undo
1333306 Support platform specific message in keyboard shortcuts dialog
6bfbf53 Collapse block slugs and expand on hover/focus
ed33efb Slightly strong shading on slug hover target
4513d9c ve.ce.Node: Clean up whitespace in rgba?() syntax
8a4da8e Make the 'full size' button optional
3530f8d ve.ce.Node: Don't use padding or height in the slug transition
d3423df Support multiple shortcuts per trigger
3521fa3 Add cmd/ctrl+y as alternative shortcut for redo
873bfef Add cmd/ctrl+m as alternative shortcut for clear formatting
00b0e63 Fix rendering of multi-shortcut actions in shortcut dialog
a010dea Add Ctrl+Shift+/ shortcut for the shortcuts dialog

Change-Id: I208fba38cf6338bfc1fad2683406931071cf5f32