voyager now fails if instrument name is not VOYAGER (#279)

* voyager now fails if inst name is not VOYAGER

* more explicit error

* sick coding is bad coding

ale/drivers/voyager_drivers.py

@@ -30,7 +30,10 @@ class VoyagerCameraLabelNaifSpiceDriver(Framer, IsisLabel, NaifSpice, Driver):
 
     @property
     def spacecraft_name(self):
-        return super().spacecraft_name.replace('_', ' ')
+        name = super().spacecraft_name.replace('_', ' ')
+        if name.split(' ')[0] != "VOYAGER":
+            raise Exception("{name} for label is not a valid Voyager spacecraft name")
+        return name
 
     @property
     def pixel_size(self):