'source' is not recognized as an internal or external command, operable program or batch file.

Describe the bug
执行npm run package时抛错

'source' is not recognized as an internal or external command, operable program or batch file.
    postman-code-generators\node_modules\shelljs\src\common.js:402
          if (config.fatal) throw e;
                            ^Error: exec: 'source' is not recognized as an internal or external command,
          operable program or batch file.
          
              at Object.error (D:\projects\postman-code-generators\node_modules\shelljs\src\common.js:111:27)
              at execSync (D:\projects\postman-code-generators\node_modules\shelljs\src\exec.js:120:12)
              at Object._exec (D:\projects\postman-code-generators\node_modules\shelljs\src\exec.js:223:12)
              at Object.exec (D:\projects\postman-code-generators\node_modules\shelljs\src\common.js:336:23)
              at Object.<anonymous> (D:\projects\postman-code-generators\npm\package.js:20:20)
              at Module._compile (internal/modules/cjs/loader.js:1015:30)
              at Object.Module._extensions..js (internal/modules/cjs/loader.js:1035:10)
              at Module.load (internal/modules/cjs/loader.js:879:32)
              at Function.Module._load (internal/modules/cjs/loader.js:724:14)
              at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:60:12)

Additional context
Version of postman-code-generators/Postman app: 8.12.2
Platform: windows10
nodejs version: v12.19.0

Start with npm/package.js at line 20 and reproduce the failure using npm run package on Windows 10. Trace the shelljs command that invokes source and verify that packaging completes without the command-not-found error on the reported Node.js version.