Add mock with a legend located at y -1

Author: n-riesco

test/image/baselines/legend_negative_y.png

@@ -0,0 +1,62 @@
+{
+   "data":[
+      {
+         "x":[
+            0,
+            1,
+            2,
+            3,
+            4,
+            5,
+            6,
+            7,
+            8
+         ],
+         "y":[
+            0,
+            3,
+            6,
+            4,
+            5,
+            2,
+            3,
+            5,
+            4
+         ],
+         "type":"scatter"
+      },
+      {
+         "x":[
+            0,
+            1,
+            2,
+            3,
+            4,
+            5,
+            6,
+            7,
+            8
+         ],
+         "y":[
+            0,
+            4,
+            7,
+            8,
+            3,
+            6,
+            3,
+            3,
+            4
+         ],
+         "type":"scatter"
+      }
+   ],
+   "layout":{
+      "showlegend":true,
+      "legend":{
+         "x":1,
+         "y":-1,
+         "xanchor":"left"
+      }
+   }
+}