Update VE core submodule to master (90bb24f)

New changes:
65d4858 README: Add devDependencies badge
4d88b3a Replace boolean checks of getSlugAtOffset with hasSlugAtOffset
b0edb58 Add getNativeRange method with optional DM range argument
f59bb20 Separate computation of highlights from rendering
4face58 Remove getSelection*Client* methods
c94234a Rename inlineRects to startAndEndRects everywhere
69c42c2 Allow specification of range when getting selection rectangles
7883250 Provide a method to get all the rectangles for a given selection
c346ebd Work around Chrome's Range.getClientRects bug

Change-Id: Idb695a64353177e5e5210bae3c4202e701f4d95e