Fix partial pattern match warning for fromJust

Author: garyb

src/Data/Maybe/Unsafe.js

@@ -0,0 +1,8 @@
+/* global exports */
+"use strict";
+
+// module Data.Maybe.Unsafe
+
+exports.unsafeThrow = function (msg) {
+  throw new Error(msg);
+};

src/Data/Maybe/Unsafe.purs

@@ -9,3 +9,6 @@ import Data.Maybe
 -- | runtime.
 fromJust :: forall a. Maybe a -> a
 fromJust (Just x) = x
+fromJust Nothing = unsafeThrow "Data.Maybe.Unsafe.fromJust called on Nothing"
+
+foreign import unsafeThrow :: forall a. String -> a