Update call to warnings

Author: VeckoTheGecko

parcels/__init__.py

@@ -2,7 +2,7 @@
 
 __version__ = version
 
-import warnings
+import warnings as _warnings
 
 from parcels.application_kernels import *
 from parcels.field import *
@@ -14,7 +14,7 @@
 from parcels.particleset import *
 from parcels.tools import *
 
-warnings.warn(
+_warnings.warn(
     "This is an alpha version of Parcels v4. The API is not stable and may change without deprecation warnings.",
     UserWarning,
     stacklevel=2,