add migration tests

public/app/plugins/panel/gauge/__snapshots__/module.test.ts.snap

+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Gauge Module migrations should migrate from 6.0 settings to 6.1 1`] = `
+Object {
+  "display": Object {
+    "decimals": 4,
+    "mappings": Array [],
+    "prefix": "a",
+    "stat": "avg",
+    "suffix": "z",
+    "thresholds": Array [
+      Object {
+        "color": "green",
+        "index": 0,
+        "value": -Infinity,
+      },
+      Object {
+        "color": "red",
+        "index": 1,
+        "value": 80,
+      },
+    ],
+    "unit": "ms",
+  },
+  "maxValue": 60,
+  "minValue": 50,
+  "showThresholdLabels": false,
+  "showThresholdMarkers": true,
+  "stat": "avg",
+}
+`;