chore: downgrade vexflow to 1.2.93 again (#706)

there are still a few critical issues with the Vexflow 3x versions, see #706.
vexflow 1.2.93 has better measure layouting for measures with half notes.
also, there is no overlap of notes into the next measure.

tabs look better with 1.2.93 as well.

package.json

@@ -66,7 +66,7 @@
     "loglevel": "^1.6.8",
     "svg2pdf.js": "^1.5.0",
     "typescript-collections": "^1.3.3",
-    "vexflow": "3.0.4"
+    "vexflow": "1.2.93"
   },
   "devDependencies": {
     "@types/chai": "^4.2.11",