Set row height when char size is changed

When zoomed in line-height and actual rendered row height differs. This
can be seen in the viewport being too large when zoomed in right now
but also has additional impacts in the new selection model #207

src/xterm.js

@@ -763,7 +763,8 @@ Terminal.loadAddon = function(addon, callback) {
 Terminal.prototype.updateCharSizeCSS = function() {
   this.charSizeStyleElement.textContent =
       `.xterm-wide-char{width:${this.charMeasure.width * 2}px;}` +
-      `.xterm-normal-char{width:${this.charMeasure.width}px;}`
+      `.xterm-normal-char{width:${this.charMeasure.width}px;}` +
+      `.xterm-rows > div{height:${this.charMeasure.height}px;}`;
 }
 
 /**