Fix link in Span.md

Fix link for proper rendering and full building.

Author: Amanda Butler

docs/reference/api/platform/Span.md

@@ -88,7 +88,7 @@ When you encode the size of the sequence viewed in the Span value, Span instance
 
 ### Span class reference
 
-[![View code](https://www.mbed.com/embed/?type=library)](https://os-doc-builder.test.mbed.com/docs/development/mbed-os-api-doxy/class_span.html)
+[![View code](https://www.mbed.com/embed/?type=library)](http://os-doc-builder.test.mbed.com/docs/development/mbed-os-api-doxy/class_span.html)
 
 
 ### Span example
@@ -143,4 +143,4 @@ while (buffer_size) {
     split(&buffer_ptr, &buffer_size, &token_ptr, &token_size, ' ');
     printf("token: %.*s\r\n", token_size, token_ptr);
 }
-```
+```