fix(dashboard/overview): graphs on Safari (#1771)

There seems to be a bug in Safari with flex layout, hard coding the height of the graph seems to do the trick.

Fixes #1755

src/chartist.scss

@@ -27,6 +27,13 @@ $ct-series-colors: (
   flex-direction: column-reverse;
 }
 
+// safari has a bug in flex computing that prevent charts from showing see #1755
+// by fixing the height with a value found in Chrome it seems like it fixes the issue without breaking the layout
+// elsewhere
+.dashboardItem .ct-chart {
+  height: 150px;
+}
+
 // Line in charts with only 2px in width
 .ct-line {
   stroke-width: 2px;

src/common/tooltip/index.css

@@ -1,7 +1,7 @@
 .tooltipEnabled {
   background-color: #222;
   border-radius: 3px;
-  border: 1px solid $fff;
+  border: 1px solid #fff;
   color: #fff;
   display: inline-block;
   font-size: 13px;

src/xo-app/dashboard/overview/index.js

@@ -203,7 +203,7 @@ export default class Overview extends Component {
                 <CardHeader>
                   <Icon icon='memory' /> {_('memoryStatePanel')}
                 </CardHeader>
-                <CardBlock>
+                <CardBlock className='dashboardItem'>
                   <ChartistGraph
                     data={{
                       labels: ['Used Memory', 'Total Memory'],
@@ -227,7 +227,7 @@ export default class Overview extends Component {
                   <Icon icon='cpu' /> {_('cpuStatePanel')}
                 </CardHeader>
                 <CardBlock>
-                  <div className='ct-chart'>
+                  <div className='ct-chart dashboardItem'>
                     <ChartistGraph
                       data={{
                         labels: ['vCPUs', 'CPUs'],
@@ -252,7 +252,7 @@ export default class Overview extends Component {
                   <Icon icon='disk' /> {_('srUsageStatePanel')}
                 </CardHeader>
                 <CardBlock>
-                  <div className='ct-chart'>
+                  <div className='ct-chart dashboardItem'>
                     <BlockLink to='/dashboard/health'>
                       <ChartistGraph
                         data={{
@@ -318,7 +318,7 @@ export default class Overview extends Component {
                 <CardHeader>
                   <Icon icon='vm-force-shutdown' /> {_('vmStatePanel')}
                 </CardHeader>
-                <CardBlock>
+                <CardBlock className='dashboardItem'>
                   <BlockLink to='/home?t=VM'>
                     <ChartistGraph
                       data={{
@@ -340,7 +340,7 @@ export default class Overview extends Component {
                 <CardHeader>
                   <Icon icon='disk' /> {_('srTopUsageStatePanel')}
                 </CardHeader>
-                <CardBlock>
+                <CardBlock className='dashboardItem'>
                   <BlockLink to='/dashboard/health'>
                     <ChartistGraph
                       style={{strokeWidth: '30px'}}