Fixed characterHeight calculation, which could cause overflowing

The previous calculation was simply using the height of the letter
W, but wasn't taking into account that each row has a lineHeight,
which might be greater. If the lineHeight is .4px off, after many
rows, it will cause the proposedGeometry to have an extra row,
potentially causing hidden rows (based on layout).

src/addons/fit/fit.js

@@ -56,7 +56,7 @@
     subjectRow.innerHTML = 'W'; // Common character for measuring width, although on monospace
     characterWidth = subjectRow.getBoundingClientRect().width;
     subjectRow.style.display = ''; // Revert style before calculating height, since they differ.
-    characterHeight = parseInt(subjectRow.offsetHeight);
+    characterHeight = parseFloat(term.rowContainer.style.lineHeight);
     subjectRow.innerHTML = contentBuffer;
 
     rows = parseInt(availableHeight / characterHeight);