docs: Fix environment variable name (#32161)

The names of environment variables are case-sensitive on Linux and Mac.

Co-authored-by: stephen9357 <stephen9357@gmail.com>

docs/tutorial/installation.md

@@ -91,7 +91,7 @@ The above configuration will download from URLs such as
 `https://npm.taobao.org/mirrors/electron/8.0.0/electron-v8.0.0-linux-x64.zip`.
 
 If your mirror serves artifacts with different checksums to the official
-Electron release you may have to set `ELECTRON_USE_REMOTE_CHECKSUMS=1` to
+Electron release you may have to set `electron_use_remote_checksums=1` to
 force Electron to use the remote `SHASUMS256.txt` file to verify the checksum
 instead of the embedded checksums.