Add string delimiters for averages.

Before, if the average was equal to 0, it was displayed on the graph but the label was not displayed.
Now, the label is displayed.

app/views/stats/index.phtml

@@ -104,7 +104,7 @@ function initStats() {
 		},{
 			data: avg,
 			lines: {show: true},
-			label: <?php echo $this->average?>
+			label: "<?php echo $this->average?>"
 		}],
 		{
 			grid: {verticalLines: false},

app/views/stats/repartition.phtml

@@ -67,7 +67,7 @@ function initStats() {
 		}, {
 			data: avg_h,
 			lines: {show: true},
-			label: <?php echo $this->averageHour?>,
+			label: "<?php echo $this->averageHour?>",
 			yaxis: 2
 		}],
 		{
@@ -96,7 +96,7 @@ function initStats() {
 		}, {
 			data: avg_dow,
 			lines: {show: true},
-			label: <?php echo $this->averageDayOfWeek?>,
+			label: "<?php echo $this->averageDayOfWeek?>",
 			yaxis: 2
 		}],
 		{
@@ -126,7 +126,7 @@ function initStats() {
 		}, {
 			data: avg_m,
 			lines: {show: true},
-			label: <?php echo $this->averageMonth?>,
+			label: "<?php echo $this->averageMonth?>",
 			yaxis: 2
 		}],
 		{