add Heinke 2019 ref with doi

cannot be found on crossref since it is a phd thesis

Author: trappitsch

src/rimscode_website/data/references.json

@@ -174,5 +174,9 @@
     "10.25358/openscience-1003": {
 	"author": "Mattolat",
 	"year": 2018
+    },
+    "10.25358/openscience-2346": {
+        "author": "Heinke",
+        "year": 2019
     }
 }