Failed to include maven dependency to libraft

[dzlab]

I'm trying to include libraft in my project, by adding the following maven dependency:

<dependency>
  <groupId>io.libraft</groupId>
  <artifactId>libraft-agent</artifactId>
  <version>0.1.1</version>
</dependency>

When I issue mvn install, the project's build fail with missing dependencies to el-api:jar:2.2.+, slf4j-api:jar:1.7.+, guava:jar:14.0.+. I also see the following in the logs:

[WARNING] The POM for org.glassfish.web:el-impl:jar:2.2.+ is missing, no dependency information available
[WARNING] The POM for javax.el:el-api:jar:2.2.+ is missing, no dependency information available
[WARNING] The POM for org.slf4j:slf4j-api:jar:1.7.+ is missing, no dependency information available
[WARNING] The POM for com.google.guava:guava:jar:14.0.+ is missing, no dependency information available
[WARNING] The POM for org.slf4j:log4j-over-slf4j:jar:1.7.+ is missing, no dependency information available

Why those '+' next to the jar files?