jgitver packaging in submodules

## Issue

**version**:1.3.0

**usage context**: Apache Maven 3.5.4 (1edded0938998edf8bf061f1ceb3cfdeccf443fe; 2018-06-17T20:33:14+02:00)

**Problem description**:

- When using jgitver on a multimodule project it fails to package the correct version in submodules.

Steps to reproduce:

1) Create archetype demo1 project as from the documentation
2) Verify the correct version in target/demo1....jar:/META-INF/....pom.xml
3) Move demo1 to a sub directory and create a new parent module
4) Retry the verification in demo1/target/demo1...jar:/META-INF/...pom.xml

Example below:

```
mvn archetype:generate -B \
-DarchetypeCatalog=internal \
-DarchetypeGroupId=org.apache.maven.archetypes \
-DarchetypeArtifactId=maven-archetype-quickstart \
-DarchetypeVersion=1.1 \
-DgroupId=fr.brouillard.jgitver.demos \
-DartifactId=demo1 \
-Dpackage=fr.brouillard.jgitver.demos \
-Dversion=0

cd demo1

git init
git add .
git commit -m "inital commit"

// Create extensions.xml file

mvn package

jar xvf target/demo1-0.0.0-SNAPSHOT.jar META-INF/maven/fr.brouillard.jgitver.demos/demo1/pom.xml
head META-INF/maven/fr.brouillard.jgitver.demos/demo1/pom.xml

4.0.0
fr.brouillard.jgitver.demos
demo1
**0.0.0-SNAPSHOT**
demo1
http://maven.apache.org



mkdir demo1
mv src demo1
mv pom.xml demo1

**create new pom.xml:**

4.0.0

fr.brouillard.jgitver.demos
demo1-parent
0
pom

demo1




mvn package

[INFO] no suitable configuration file found, using defaults
[INFO] Scanning for projects...
[INFO] Using jgitver-maven-plugin [1.3.0] (sha1: ef8eec9f820d662e63a84f1210c377183e450cbd)
[INFO] jgitver-maven-plugin is about to change project(s) version(s)
[INFO] fr.brouillard.jgitver.demos::demo1-parent::0 -> 0.0.0-SNAPSHOT
[INFO] fr.brouillard.jgitver.demos::demo1::0 -> 0.0.0-SNAPSHOT

jar xvf demo1/target/demo1-0.0.0-SNAPSHOT.jar META-INF/maven/fr.brouillard.jgitver.demos/demo1/pom.xml
head META-INF/maven/fr.brouillard.jgitver.demos/demo1/pom.xml

4.0.0

fr.brouillard.jgitver.demos
demo1
**0**
jar

demo1

```

Reproduce the reported behavior with the generated parent pom.xml, child demo1/pom.xml, and extensions.xml setup, then inspect the packaged META-INF/maven/.../pom.xml inside demo1/target/demo1-0.0.0-SNAPSHOT.jar. Confirm that the child POM records the computed 0.0.0-SNAPSHOT version rather than the original 0, and use the Maven package output to compare standalone and multimodule builds.

Written by the indexing model from the issue text.