npm.bbclass: Fix file permissions before opening it for writing

Some node module archives in npmjs.org contain wrong permissions.
I found a case with package.json in the archive being r-xr-xr-x
for which open(..., "w") fails. Modify the manifest file permissions
to add the write bit for the owner.

(From OE-Core rev: c6740091cb7336aaa3bb9b692fe4dc6fc92aa3a8)

Signed-off-by: Zoltán Böszörményi <zboszor@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes/npm.bbclass

@@ -81,6 +81,7 @@ python npm_do_configure() {
     import json
     import re
     import shlex
+    import stat
     import tempfile
     from bb.fetch2.npm import NpmEnvironment
     from bb.fetch2.npm import npm_unpack
@@ -202,6 +203,7 @@ python npm_do_configure() {
         if has_shrinkwrap_file:
             _update_manifest("devDependencies")
 
+    os.chmod(cached_manifest_file, os.stat(cached_manifest_file).st_mode | stat.S_IWUSR)
     with open(cached_manifest_file, "w") as f:
         json.dump(cached_manifest, f, indent=2)