Update snap include path instruction (google#5297)

Author: om26er

snap/snapcraft.yaml

@@ -10,7 +10,7 @@ description: |
   projects using flatbuffers, however, for the compilation to work, you have
   to manually add the following path in your project's configuration:
 
-  /snap/flatc/current/include
+  /snap/flatbuffers/current/include
 
   If you need to use flatbuffers headers from a location other than the above
   path, it is recommended to not use this snap as that could cause a mismatch.