Fix example bug

Author: lukelbd

docs/subplots.ipynb

@@ -188,7 +188,7 @@
     "N = 50\n",
     "M = 40\n",
     "state = np.random.RandomState(51423)\n",
-    "colors = plot.colors('grays_r', M, left=0.1, right=0.8)\n",
+    "colors = plot.Colors('grays_r', M, left=0.1, right=0.8)\n",
     "datas = []\n",
     "for scale in (1, 3, 7, 0.2):\n",
     "    data = scale * (state.rand(N, M) - 0.5).cumsum(axis=0)[N//2:, :]\n",