fix copy assets progress by moving fetch_add out of trace!().

[liigo]

before this PR: (note the six (0/6))

  15.509s  INFO Bundling app...
  15.536s  INFO Running wasm-bindgen...
  15.790s  INFO Copying asset (0/6): C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\header.svg
  15.791s  INFO Copying asset (0/6): \\?\C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\main.css
  15.792s  INFO Copying asset (0/6): C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\favicon.ico
  15.794s  INFO Copying asset (0/6): \\?\C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\favicon.ico
  15.795s  INFO Copying asset (0/6): \\?\C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\header.svg
  15.797s  INFO Copying asset (0/6): C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\main.css
  19.87s  INFO Copying app to output directory...

after this PR:

1258.16s  INFO Bundling app...
1258.18s  INFO Running wasm-bindgen...
1260.72s  INFO Copying asset (1/6): C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\favicon.ico
1260.73s  INFO Copying asset (0/6): \\?\C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\favicon.ico
1260.75s  INFO Copying asset (4/6): C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\header.svg
1260.76s  INFO Copying asset (2/6): \\?\C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\main.css
1260.76s  INFO Copying asset (5/6): C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\main.css
1260.77s  INFO Copying asset (3/6): \\?\C:\Users\liigo\tmp\hidx06\Bare-Bones\assets\header.svg
1283. 2s  INFO Copying app to output directory...