fix: Use LAUNCHDARKLY_SDK_KEY instead

Author: louis-launchdarkly

README.md

@@ -10,10 +10,10 @@ For a sample application demonstrating how to use LaunchDarkly in *client-side*
 
 ## Build instructions
 
-1. Set the environment variable `LAUNCHDARKLY_SERVER_KEY` to your LaunchDarkly SDK key. If there is an existing boolean feature flag in your LaunchDarkly project that you want to evaluate, set `LAUNCHDARKLY_FLAG_KEY` to the flag key; otherwise, a boolean flag of `sample-feature` will be assumed.
+1. Set the environment variable `LAUNCHDARKLY_SDK_KEY` to your LaunchDarkly SDK key. If there is an existing boolean feature flag in your LaunchDarkly project that you want to evaluate, set `LAUNCHDARKLY_FLAG_KEY` to the flag key; otherwise, a boolean flag of `sample-feature` will be assumed.
 
     ```bash
-    export LAUNCHDARKLY_SERVER_KEY="1234567890abcdef"
+    export LAUNCHDARKLY_SDK_KEY="1234567890abcdef"
     export LAUNCHDARKLY_FLAG_KEY="my-boolean-flag"
     ```