Remove use gulp.start()

gulp.start() is never officially supported by gulp, it's better to use the functionality provided by gulp.watch(). 

See: gulpjs/gulp#755

gulpfile.babel.js

@@ -7,7 +7,6 @@ import postcss from "gulp-postcss";
 import cssImport from "postcss-import";
 import cssnext from "postcss-cssnext";
 import BrowserSync from "browser-sync";
-import watch from "gulp-watch";
 import webpack from "webpack";
 import webpackConfig from "./webpack.conf";
 
@@ -63,10 +62,10 @@ gulp.task("server", ["hugo", "css", "js", "fonts"], () => {
       baseDir: "./dist"
     }
   });
-  watch("./src/js/**/*.js", () => { gulp.start(["js"]) });
-  watch("./src/css/**/*.css", () => { gulp.start(["css"]) });
-  watch("./src/fonts/**/*", () => { gulp.start(["fonts"]) });
-  watch("./site/**/*", () => { gulp.start(["hugo"]) });
+  gulp.watch("./src/js/**/*.js", ["js"]);
+  gulp.watch("./src/css/**/*.css", ["css"]);
+  gulp.watch("./src/fonts/**/*", ["fonts"]);
+  gulp.watch("./site/**/*", ["hugo"]);
 });
 
 /**