Add support to compose only functions in utils/compose (reduxjs#2073)

* Add support to compose only functions in utils/compose

* Remove some parens

Author: evilj0e

src/compose.js

@@ -14,6 +14,8 @@ export default function compose(...funcs) {
     return arg => arg
   }
 
+  funcs = funcs.filter(func => typeof func === 'function')
+
   if (funcs.length === 1) {
     return funcs[0]
   }

test/compose.spec.js

@@ -21,6 +21,17 @@ describe('Utils', () => {
       expect(compose(c, a, b)(final)('')).toBe('cab')
     })
 
+    it('composes only functions', () => {
+      const square = x => x * x
+      const add = (x, y) => x + y
+      
+      expect(compose(square, add, false)(1, 2)).toBe(9)
+      expect(compose(square, add, undefined)(1, 2)).toBe(9)
+      expect(compose(square, add, true)(1, 2)).toBe(9)
+      expect(compose(square, add, NaN)(1, 2)).toBe(9)
+      expect(compose(square, add, '42')(1, 2)).toBe(9)
+    })
+
     it('can be seeded with multiple arguments', () => {
       const square = x => x * x
       const add = (x, y) => x + y