docs: fix Mathjax startup (#249)

### Summary of Changes

Update the MathJax config script, so math blocks get rendered properly
already the first time a page is visited.

Author: lars-reimann

docs/javascript/mathjax.js

@@ -11,6 +11,9 @@ window.MathJax = {
     },
 };
 
-document$.subscribe(() => {
+ocument$.subscribe(() => {
+    MathJax.startup.output.clearCache();
+    MathJax.typesetClear();
+    MathJax.texReset();
     MathJax.typesetPromise();
 });