Fix copying of binary files during asset build

This fixes another instance of the issue identified in
hypothesis/client#6527.

Fixes #8952

gulpfile.js

@@ -45,7 +45,10 @@ const fontFiles = 'h/static/styles/vendor/fonts/h.woff';
 
 gulp.task('build-fonts', () => {
   const fontsDir = 'build/fonts';
-  return gulp.src(fontFiles).pipe(changed(fontsDir)).pipe(gulp.dest(fontsDir));
+  return gulp
+    .src(fontFiles, { encoding: false })
+    .pipe(changed(fontsDir))
+    .pipe(gulp.dest(fontsDir));
 });
 
 gulp.task('watch-fonts', () => {
@@ -75,7 +78,7 @@ gulp.task('build-images', () => {
 
   const imagesDir = 'build/images';
   return gulp
-    .src(imageFiles)
+    .src(imageFiles, { encoding: false })
     .pipe(changed(imagesDir))
     .pipe(gulpIf(shouldMinifySVG, svgmin(svgminConfig)))
     .pipe(gulp.dest(imagesDir));