Quote $PATH export to account for spaces.

Many people have spaces in their Windows user names, leading to trouble with an unquoted $PATH export.  This quotes the $PATH addition accordingly.

setup/swc-windows-installer.py

@@ -83,7 +83,7 @@ def update_bash_profile(extra_paths=()):
     lines = [
         '',
         '# Add paths for Software-Carpentry-installed scripts and executables',
-        'export PATH=$PATH:{}'.format(':'.join(
+        'export PATH=\"$PATH:{}\"'.format(':'.join(
             make_posix_path(path) for path in extra_paths),),
         '',
         '# Make nano the default editor',