Use curly brackets around hyperlink help text #11478 (#11479)

public/app/plugins/panel/table/column_options.html

@@ -163,10 +163,10 @@
           <span>
             Use special variables to specify cell values:
             <br>
-            <em>$__cell</em> refers to current cell value
+            <em>${__cell}</em> refers to current cell value
             <br>
-            <em>$__cell_n</em> refers to Nth column value in current row. Column indexes are started from 0. For instance,
-            <em>$__cell_1</em> refers to second column's value.
+            <em>${__cell_n}</em> refers to Nth column value in current row. Column indexes are started from 0. For instance,
+            <em>${__cell_1}</em> refers to second column's value.
           </span>
         </info-popover>
       </div>