bpo-22589 Changed MIME type of .bmp to "image/bmp" (#4756)

Per rfc7903 this is the standard MIME type for this file format, and appears as such in the IANA MIME registry.
diff --git a/Lib/mimetypes.py b/Lib/mimetypes.py
index 4411202..c86dd6d 100644
--- a/Lib/mimetypes.py
+++ b/Lib/mimetypes.py
@@ -410,7 +410,7 @@
         '.bat'    : 'text/plain',
         '.bcpio'  : 'application/x-bcpio',
         '.bin'    : 'application/octet-stream',
-        '.bmp'    : 'image/x-ms-bmp',
+        '.bmp'    : 'image/bmp',
         '.c'      : 'text/plain',
         '.cdf'    : 'application/x-netcdf',
         '.cpio'   : 'application/x-cpio',