Fix passing shape (2,) input to Collections.set_offsets.

The logic with uniform_offsets seems a bit crazy but let's just reproduce it for now...
matplotlib · tacaswell · Sep 28, 2017 · Sep 26, 2017 · Sep 28, 2017 · c5170ec00f6b7b725ad63e68f95f12fd5666efcd
commit c5170ec00f6b7b725ad63e68f95f12fd5666efcd
diff --git a/lib/matplotlib/collections.py b/lib/matplotlib/collections.py
@@ -143,10 +143,13 @@ def __init__(self,
        self.set_offset_position(offset_position)
        self.set_zorder(zorder)

+        self._offsets = np.zeros((1, 2))
        self._uniform_offsets = None
-        self._offsets = np.array([[0, 0]], float)
        if offsets is not None:
            offsets = np.asanyarray(offsets, float)
+            # Broadcast (2,) -> (1, 2) but nothing else.
+            if offsets.shape == (2,):
+                offsets = offsets[None, :]
            if transOffset is not None:
                self._offsets = offsets
                self._transOffset = transOffset
@@ -400,7 +403,7 @@ def set_hatch(self, hatch):
        self.stale = True

    def get_hatch(self):
-        'Return the current hatching pattern'
+        """Return the current hatching pattern."""
        return self._hatch

    def set_offsets(self, offsets):
@@ -411,18 +414,18 @@ def set_offsets(self, offsets):
        ACCEPTS: float or sequence of floats
        """
        offsets = np.asanyarray(offsets, float)
-        #This decision is based on how they are initialized above
+        if offsets.shape == (2,):  # Broadcast (2,) -> (1, 2) but nothing else.
+            offsets = offsets[None, :]
+        # This decision is based on how they are initialized above in __init__.
        if self._uniform_offsets is None:
            self._offsets = offsets
        else:
            self._uniform_offsets = offsets
        self.stale = True

    def get_offsets(self):
-        """
-        Return the offsets for the collection.
-        """
-        #This decision is based on how they are initialized above in __init__()
+        """Return the offsets for the collection."""
+        # This decision is based on how they are initialized above in __init__.
        if self._uniform_offsets is None:
            return self._offsets
        else: