update version in docs

[maven-release-plugin] copy for tag WebMagic-0.5.1

[maven-release-plugin] copy for tag WebMagic-0.5.0

[maven-release-plugin] copy for tag webmaigc-0.4.3

[maven-release-plugin] copy for tag webmagic-0.4.2

[maven-release-plugin] copy for tag webmagic-0.4.1

[maven-release-plugin] copy for tag webmagic-0.4.0

[maven-release-plugin] copy for tag webmagic-0.3.2

[maven-release-plugin] copy for tag webmagic-parent-0.3.1

[maven-release-plugin] copy for tag webmagic-0.3.0