Rename Erratic.json to ErraticInstruments.json

slug <-> filename mismatch
repo-pointer needs an update too

ref: #443

manifests/Erratic.json → manifests/ErraticInstruments.json

@@ -6,4 +6,4 @@
   "manualUrl": "https://github.com/bafonso/Erratic/blob/master/README.md",
   "sourceUrl": "https://github.com/bafonso/Erratic",
   "repoVersion": "0.6.0"
-}
+}