Merge pull request JiaweiZhuang#71 from pangeo-data/link-doc-fix

fix broken link in doc notebook masking/extrapolation

doc/notebooks/Masking.ipynb

@@ -606,7 +606,7 @@
     "As we saw in the previous example, the bilinear interpolation was not providing\n",
     "a value at all the destination points. This is where the extrapolation becomes\n",
     "useful. xESMF allows to use the ESMF algorithms described in this\n",
-    "[section of the ESMF documentation](http://www.earthsystemmodeling.org/esmf_releases/public/ESMF_8_0_0/ESMF_refdoc/node5.html#sec:extrapolation:overview).\n",
+    "[section of the ESMF documentation](http://earthsystemmodeling.org/docs/release/ESMF_8_0_1/ESMF_refdoc/node9.html#SECTION090117000000000000000).\n",
     "This is a very short example and more options are available. Please refer to the\n",
     "aforementioned documentation for more details.\n"
    ]