Convert British spelling to American

tools/i-pi/ipi/engine/atoms.py

@@ -51,7 +51,7 @@ class Atom(dobject):
    """
 
    def __init__(self, system, index):
-      """Initialises Atom.
+      """Initializes Atom.
 
       Args:
          system: An Atoms object containing the required atom.
@@ -116,7 +116,7 @@ class Atoms(dobject):
 
 
    def __init__(self, natoms, _prebind=None):
-      """Initialises Atoms.
+      """Initializes Atoms.
 
       Each replica and the centroid coordinate are all held as Atoms objects,
       and so slices of the global position and momentum arrays must be used in