Trust gsutil on more content-types

It appears to use `file -b --mime`. The only file types this gives me
an unexpected result for are glsl and wgsl

https://github.com/GoogleCloudPlatform/gsutil/blob/a872f98b59bad2bb72010afb9b0b90aa91ec5d0c/gslib/utils/copy_helper.py#L1702

build-and-release.bash

@@ -12,6 +12,7 @@ cp build/rendering-playground.html "build/rendering-playground-${VERSION}.html"
 ls -- build
 
 gsutil \
+  -m \
   -h "Content-Type:text/plain" \
   cp \
   -Z \
@@ -20,23 +21,11 @@ gsutil \
   gs://maze-playground/
 
 gsutil \
-  -h "Content-Type:application/wasm" \
-  cp \
-  -Z \
-  build/*.wasm \
-  gs://maze-playground/
-
-gsutil \
-  -h "Content-Type:application/json" \
+  -m \
   cp \
   -Z \
   build/*.js.map \
   build/*.css.map \
-  gs://maze-playground/
-
-gsutil \
-  cp \
-  -Z \
   build/*.js \
   build/*.css \
   build/*.html \