Fix typo (dotnet#4271)

* Fix typo

* Fix typo

Author: mairaw

samples/snippets/csharp/VS_Snippets_CLR_System/system.Double.Parse/cs/Parse3.cs

@@ -5,7 +5,7 @@
 public class Temperature
 {
    // Parses the temperature from a string. Temperature scale is
-   // indicated by 'F (for Fahrenheit) or 'C (for Celcius) at the end
+   // indicated by 'F (for Fahrenheit) or 'C (for Celsius) at the end
    // of the string.
    public static Temperature Parse(string s, NumberStyles styles,
                                    IFormatProvider provider)

samples/snippets/visualbasic/VS_Snippets_CLR_System/system.Double.Parse/vb/Parse3.vb

@@ -6,7 +6,7 @@ Imports System.Globalization
 
 Public Class Temperature
    ' Parses the temperature from a string. Temperature scale is 
-   ' indicated by 'F (for Fahrenheit) or 'C (for Celcius) at the end
+   ' indicated by 'F (for Fahrenheit) or 'C (for Celsius) at the end
    ' of the string.
    Public Shared Function Parse(s As String, styles As NumberStyles, _
                                 provider As IFormatProvider) As Temperature