In tooltip x align calculation take into account caretSize

Truncation up to caretSize pixels could happen if label text produced tooltip element with size width:
* left side tooltip: width < x and width > x - caretSize
* right side tooltip: width < chartWidth - x and width > chartWidth - x - caretSize
Default caretSize = 5, so with default configuration truncation up to 5 pixels could happen.

src/core/core.tooltip.js

@@ -291,10 +291,10 @@ module.exports = function(Chart) {
 		}
 
 		olf = function(x) {
-			return x + size.width > chart.width;
+			return x + size.width + model.caretSize > chart.width;
 		};
 		orf = function(x) {
-			return x - size.width < 0;
+			return x - size.width - model.caretSize < 0;
 		};
 		yf = function(y) {
 			return y <= midY ? 'top' : 'bottom';