add image tests for sqrt errorbars

Author: etpinard

test/image/baselines/error_bar_sqrt.png

@@ -0,0 +1,22 @@
+{
+  "data": [
+    {
+      "x": [
+        1,
+        2,
+        3,
+        4
+      ],
+      "y": [
+        2,
+        1,
+        3,
+        4
+      ],
+      "error_y": {
+        "type": "sqrt"
+      },
+      "type": "scatter"
+    }
+  ]
+}

test/image/baselines/gl3d_errorbars_sqrt.png

@@ -0,0 +1,56 @@
+{
+    "data": [
+        {
+            "type": "scatter3d",
+            "x": [
+                1,
+                2,
+                3
+            ],
+            "y": [
+                1,
+                2,
+                3
+            ],
+            "z": [
+                16,
+                4,
+                16
+            ],
+            "error_z": {
+                "array": [
+                    2,
+                    4,
+                    2
+                ],
+                "value": 2,
+                "width": 10
+            },
+            "error_x": {
+                "type": "sqrt",
+                "width": 5
+            },
+            "uid": "10ccaa"
+        }
+    ],
+    "layout": {
+        "title": "sqrt errorbars",
+        "scene": {
+            "camera": {
+                "eye": {
+                    "x": 1.5,
+                    "y": -1.5,
+                    "z": 1
+                }
+            },
+            "aspectratio": {
+                "x": 2,
+                "y": 2,
+                "z": 1
+            }
+        },
+        "height": 450,
+        "width": 1000,
+        "autosize": true
+    }
+}