出现这个问题是因为我用的angular版本是1.5.

This problem happened because the angular version I am using is 1.5.

将可执行文件从 npm 更改为 npm.cmd 解决了问题！

changing the executable from npm to npm.cmd solved the problem!

<execution>
                <id>exec-npm-update</id>
                <phase>generate-sources</phase>
                <configuration>
                  <workingDirectory>${uiResourcesDir}</workingDirectory>
                  <executable>npm.cmd</executable>
                  <arguments>
                    <argument>update</argument>
                  </arguments>
                </configuration>
                <goals>
                  <goal>exec</goal>
                </goals>
              </execution>