Update example in FileSystem.md

Change example link because this appears to be the up-to-date of the out-of-sync repos.

Author: Amanda Butler

docs/api/storage/FileSystem.md

@@ -20,7 +20,7 @@ For details regarding how to configure the default file system or override its i
 
 ### File system example
 
-[![View code](https://www.mbed.com/embed/?url=https://os.mbed.com/teams/mbed-os-examples/code/mbed-os-example-filesystem/)](https://os.mbed.com/teams/mbed-os-examples/code/mbed-os-example-filesystem/file/bc8560ba955d/main.cpp)
+[![View code](https://www.mbed.com/embed/?url=https://github.com/ARMmbed/mbed-os-example-filesystem/)](https://github.com/ARMmbed/mbed-os-example-filesystem/blob/master/main.cpp)
 
 ### Sector requirements