feat: add Jenkins build number support (#373)

Jenkins stores the build number in the `BUILD_NUMBER` environment variable

Author: Tim Cooper

src/platformPackager.ts

@@ -205,7 +205,7 @@ export abstract class PlatformPackager<DC extends PlatformSpecificBuildOptions>
   }
 
   protected computeBuildNumber(): string {
-    return this.devMetadata.build["build-version"] || process.env.TRAVIS_BUILD_NUMBER || process.env.APPVEYOR_BUILD_NUMBER || process.env.CIRCLE_BUILD_NUM
+    return this.devMetadata.build["build-version"] || process.env.TRAVIS_BUILD_NUMBER || process.env.APPVEYOR_BUILD_NUMBER || process.env.CIRCLE_BUILD_NUM || process.env.BUILD_NUMBER
   }
 
   private getOSXResourcesDir(appOutDir: string): string {
@@ -262,4 +262,4 @@ export function normalizeTargets(targets: Array<string> | string): Array<string>
   else {
     return (Array.isArray(targets) ? targets : [targets]).map(it => it.toLowerCase().trim())
   }
-}
+}