Fix unrelated PEP8 warnings

These warnings come up on CI, but not related to the other changes in
this PR.

Author: matthew-brett

nibabel/funcs.py

@@ -138,7 +138,7 @@ def concat_images(images, check_affines=True, axis=None):
                     i, len(img.shape), n_dim))
         if not np.all(np.array(img.shape)[idx_mask] == masked_shape):
             raise ValueError('shape {0} for image {1} not compatible with '
-                             'first image shape {2} with axis == {0}'.format(
+                             'first image shape {2} with axis == {3}'.format(
                                  img.shape, i, shape0, axis))
         if check_affines and not np.all(img.affine == affine):
             raise ValueError('Affine for image {0} does not match affine '

nibabel/viewers.py

@@ -184,7 +184,8 @@ def __init__(self, data, affine=None, axes=None, title=None):
                                                 5).astype(int)))
             ax.set_xlim(x[0], x[-1])
             yl = [self._data.min(), self._data.max()]
-            yl = [l + s * np.diff(lims)[0] for l, s in zip(yl, [-1.01, 1.01])]
+            yl = [L + s * np.diff(lims)[0]
+                  for L, s in zip(yl, [-1.01, 1.01])]
             patch = mpl_patch.Rectangle([-0.5, yl[0]], 1., np.diff(yl)[0],
                                         fill=True, facecolor=(0, 1, 0),
                                         edgecolor=(0, 1, 0), alpha=0.25)