broken dependency in digdag-client

[yoyama]

I got a report from TD internal about broken dependency of digdag-client.
It may need javax.servlet-api as dependency.
Need an investigation and fix it if needed.

When a user try to call io.digdag.client.DigdagClient.getProject(String), it failed as follows

NoClassDefFoundError was found with message javax/servlet/ServletContextjava.lang.NoClassDefFoundError: javax/servlet/ServletContext

---- Debugging information ----
* trace-exception   : java.lang.NoClassDefFoundError 
	at org.jboss.resteasy.plugins.interceptors.encoding.GZIPDecodingInterceptor.getMaxSize(GZIPDecodingInterceptor.java:135)
	at org.jboss.resteasy.plugins.interceptors.encoding.GZIPDecodingInterceptor.aroundReadFrom(GZIPDecodingInterceptor.java:107)
	at org.jboss.resteasy.core.interception.AbstractReaderInterceptorContext.proceed(AbstractReaderInterceptorContext.java:59)
	at org.jboss.resteasy.client.jaxrs.internal.ClientResponse.readFrom(ClientResponse.java:266)
	at org.jboss.resteasy.client.jaxrs.internal.ClientResponse.readEntity(ClientResponse.java:196)
	at org.jboss.resteasy.specimpl.BuiltResponse.readEntity(BuiltResponse.java:218)
	at io.digdag.client.DigdagClient.doGet(DigdagClient.java:958)
	at io.digdag.client.DigdagClient.getProject(DigdagClient.java:292)
	at com.treasuredata.tdautomation.equipments.DigDagClientHandler.projectByNameLocal(DigDagClientHandler.java:232)