Update tools/fuchsia/local-sdk.py

The script stopped working with more recent versions of Fuchsia.
packages/gn/gen.py now expects full path for --modules argument. Updated
the script to pass full path for packages/gn/sdk.

Change-Id: I32c511cae73075a7b37c26035e8bea764605a332
Reviewed-on: https://chromium-review.googlesource.com/683342Reviewed-by: Scott Graham <scottmg@chromium.org>
Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504408}

tools/fuchsia/local-sdk.py

@@ -43,7 +43,7 @@ def main(args):
   os.chdir(fuchsia_root)
   Run('scripts/build-zircon.sh', '-t', 'x86_64')
   Run('scripts/build-zircon.sh', '-t', 'aarch64')
-  Run('packages/gn/gen.py', '--target_cpu=x86-64', '--modules=sdk',
+  Run('packages/gn/gen.py', '--target_cpu=x86-64', '--modules=packages/gn/sdk',
       '--ignore-skia', '--release')
   Run('packages/gn/build.py', '--release')
   tempdir = tempfile.mkdtemp()