DOC: Remove space after directive name, before double-colon..

While Sphinx/Docutils allow space after the directive name, it is not in
the spec and not supported by all Rst parsers.

Those are also the only 3 place in the codebase I could find that use
space after a directive name.

Author: Carreau

lib/matplotlib/image.py

@@ -1572,7 +1572,7 @@ def imsave(fname, arr, vmin=None, vmax=None, cmap=None, format=None,
     RGB(A) images are passed through.  Single channel images will be
     colormapped according to *cmap* and *norm*.
 
-    .. note ::
+    .. note::
 
        If you want to save a single channel image as gray scale please use an
        image I/O library (such as pillow, tifffile, or imageio) directly.

src/ft2font_wrapper.cpp

@@ -325,11 +325,11 @@ const char *PyFT2Font_init__doc__ =
     "    Must be positive. Used to scale the hinting in the x-direction\n"
     "_fallback_list : list of FT2Font, optional\n"
     "    A list of FT2Font objects used to find missing glyphs.\n\n"
-    "    .. warning ::\n"
+    "    .. warning::\n"
     "        This API is both private and provisional: do not use it directly\n\n"
     "_kerning_factor : int, optional\n"
     "    Used to adjust the degree of kerning.\n\n"
-    "    .. warning ::\n"
+    "    .. warning::\n"
     "        This API is private: do not use it directly\n\n"
     "Attributes\n"
     "----------\n"