task.md: Spelling

Singular-ize to match the icons descriptions above

Author: rwp0

Introduction/Task Description/task.md

@@ -11,7 +11,7 @@ Use Task Description icons for the following actions:
 | Icon                               | Description                   |
 |------------------------------------|-------------------------------|
 |**Check**                           | <font size="-1">Check the correctness of your answer (for a quiz) or your code solution (for a programming task)</font>|   
-| **Run**                            | <font size="-1">Run your code (for a theoretical tasks)</font>|
+| **Run**                            | <font size="-1">Run your code (for a theoretical task)</font>|
 |![](images/back.svg)                | <font size="-1">Go to the previous task</font>       |    
 |![](images/forward.svg) &nbsp;<font size="-1">or</font> **Next** | <font size="-1">Go to the next task</font>| 
 |![](images/reset.svg)               | <font size="-1">Discard all the changes you’ve made in the task, and start over</font>| 
@@ -39,4 +39,4 @@ th, td {
 table td:nth-child(1) {
     text-align: center;
 }
-</style>
+</style>