fix:修正package.json配置自定义编译条件覆盖为false

如果有package.json下的uni-app->scripts配置有两个平台以上且有相同的自定义编译条件变量时会导致变量覆盖为false

packages/uni-cli-shared/lib/package.js

@@ -35,7 +35,9 @@ module.exports = {
         if (scriptName !== name) {
           const define = uniAppOptions.scripts[scriptName].define
           Object.keys(define).forEach(name => {
-            define[name] = false
+            if (typeof scriptOptions.define[name] === "undefined") {
+              define[name] = false
+            }
           })
           Object.assign(scriptOptions.define, define)
         }
@@ -50,4 +52,4 @@ module.exports = {
 
     return scriptOptions
   }
-}
+}