Handle negative numbers in tokenPreprocessor

Would still fail on things like "transform-3d" if that were ever to
come up.  An actual lexer would be the real fix rather than further
regexp hackery.

src/preprocessors/tokenPreprocessor.js

@@ -17,7 +17,7 @@ export function createTokenPreprocessor(options = { }) {
     const propsInfo = [ ];
 
     for (let prop of props) {
-      const parts = state[prop].split(/\b(\d+(?:\.\d+|\.)?|\.\d+)/);
+      const parts = state[prop].split(/(-?\b(?:\d+(?:\.\d+|\.)?|\.\d+))/);
       const values = [ ];
 
       if (typeof easing[prop] === 'string' && easing[prop].match(/\s/)) {

test/preprocessors/tokenPreprocessor.spec.js

@@ -72,4 +72,16 @@ describe('tokenPreprocessor', () => {
     expect(decode({ x__0: 3 }))
       .toEqual({ x: 'transform3d(3.00px)' });
   });
+
+  it('handles negative numbers', () => {
+    const tokenPreprocessor = createTokenPreprocessor();
+
+    const [ outState, outEasing, decode ] =
+            tokenPreprocessor({ x: 'transform3d(-2.54px)' }, { x: [ identity ] });
+
+    expect(outState).toEqual({ x__0: -2.54 });
+    expect(outEasing).toEqual({ x__0: identity });
+    expect(decode({ x__0: 3 }))
+      .toEqual({ x: 'transform3d(3.00px)' });
+  });
 });