fix: actually, let nextjs handle the node_env

Author: KatoakDR

.env.example

@@ -5,11 +5,6 @@
 # the webpack config using the `EnvironmentPlugin`.
 # ------------------------------------------------------------------------------
 
-# The environment the app is running in.
-# Generally, this should stay as 'production' so that webpack and the bundlers
-# know to optimize the build for best performance.
-NODE_ENV="production"
-
 # App-specific environment variable.
 # Similar purpose as NODE_ENV but for our own use, and at times
 # may not be in sync with the NODE_ENV the app is running under.