Covert -> convert (#3830)

* covert -> convert

* undo remove trailing white space

Author: gewarren

xml/System/Double.xml

@@ -202,7 +202,7 @@
  [!code-csharp[System.Double.Structure#20](~/samples/snippets/csharp/VS_Snippets_CLR_System/system.double.structure/cs/convert1.cs#20)]
  [!code-vb[System.Double.Structure#20](~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.double.structure/vb/convert1.vb#20)]  
   
- In addition, the <xref:System.Single> values <xref:System.Single.NaN?displayProperty=nameWithType>, <xref:System.Single.PositiveInfinity?displayProperty=nameWithType>, and <xref:System.Single.NegativeInfinity?displayProperty=nameWithType> covert to <xref:System.Double.NaN?displayProperty=nameWithType>, <xref:System.Double.PositiveInfinity?displayProperty=nameWithType>, and <xref:System.Double.NegativeInfinity?displayProperty=nameWithType>, respectively.  
+ In addition, the <xref:System.Single> values <xref:System.Single.NaN?displayProperty=nameWithType>, <xref:System.Single.PositiveInfinity?displayProperty=nameWithType>, and <xref:System.Single.NegativeInfinity?displayProperty=nameWithType> convert to <xref:System.Double.NaN?displayProperty=nameWithType>, <xref:System.Double.PositiveInfinity?displayProperty=nameWithType>, and <xref:System.Double.NegativeInfinity?displayProperty=nameWithType>, respectively.  
   
  Note that the conversion of the value of some numeric types to a <xref:System.Double> value can involve a loss of precision. As the example illustrates, a loss of precision is possible when converting <xref:System.Decimal>, <xref:System.Int64>, <xref:System.Single>, and <xref:System.UInt64> values to <xref:System.Double> values.