Fixes dotnet#987 (dotnet#993)

Fixes dotnet#987
Missing table part was just a production mishap.
Fixes the typo IFormatable -> IFormattable

Author: Nigel-Ecma

standard/standard-library.md

@@ -584,7 +584,7 @@ namespace System
 
 ## C.4 Format Specifications
 
-The meaning of the formats, as used in interpolated string expressions ([§12.8.3](expressions.md#1283-interpolated-string-expressions)), are defined in ISO/IEC 23271:2012. For convenience the following text is copied from the description of `System.IFormatable`.
+The meaning of the formats, as used in interpolated string expressions ([§12.8.3](expressions.md#1283-interpolated-string-expressions)), are defined in ISO/IEC 23271:2012. For convenience the following text is copied from the description of `System.IFormattable`.
 
 **This text is informative.**