build.sbt我的文件中的片段：
EclipseKeys.configurations := Set(Compile, Test, Provided)
unmanagedBase in Provided := new java.io.File("/path/to/external/libdir")
但是当我跑步时，sbt eclipse我得到了这个：
[info] About to create Eclipse project files for your project(s).
[error] Could not create Eclipse project files:
[error] Undefined setting 'unmanagedSourceDirectories'!
[error] Undefined task 'externalDependencyClasspath' for 'myproject'!