Fix Snapshot branchname strategy (#50)

Description
===========

The `PartialSemVerStrategy` `STAGE_BRANCH_NAME` tries to generate a
unique semver 2.0 prerelease pattern. The provided tests where mostly
written in an optimistic fashion. This patch fixes the strategy when
branch names are in use which contain unusual characters or character
combinations.

As an example:

The branchName `feature/button_01` would yield a prerelease part of:
`branch.feature.button.01` which is not semver 2 compatible. Numerical
parts are not allowed to be `0` padded. The strategy also kept hanging
characters like `-`,`+`,`_`.

This patch tries to fix this cases.

_excerpt from the tests in `ReleasePluginSpec`

```
_  | 10   | "ci"  | _  | "test/build01-"            | "1.1.0-branch.test.build.1.10"
_  | 22   | "ci"  | _  | "test/build01+"            | "1.1.0-branch.test.build.1.22"
_  | 45   | "ci"  | _  | "test/build01_"            | "1.1.0-branch.test.build.1.45"
_  | 204  | "ci"  | _  | "test/build01"             | "1.1.0-branch.test.build.1.204"
_  | 100  | "ci"  | _  | "test/build.01"            | "1.1.0-branch.test.build.1.100"
_  | 55   | "ci"  | _  | "test/build002"            | "1.1.0-branch.test.build.2.55"
_  | 66   | "ci"  | _  | "test/build.002"           | "1.1.0-branch.test.build.2.66"
_  | 789  | "ci"  | _  | "test/build000000000003"   | "1.1.0-branch.test.build.3.789"
_  | 777  | "ci"  | _  | "test/build.000000000003"  | "1.1.0-branch.test.build.3.777"
_  | 789  | "ci"  | _  | "test/build000000.000003"  | "1.1.0-branch.test.build.0.3.789"
_  | 3    | "ci"  | _  | "test/build.000000.000003" | "1.1.0-branch.test.build.0.3.3"
_  | 3    | "ci"  | _  | "release/1.00.x"           | "1.0.1-branch.release.1.0.x.3"
```

Changes
=======

![FIX] Snapshot branchname strategy

src/main/groovy/wooga/gradle/release/version/semver2/VersionStrategies.groovy

@@ -69,7 +69,19 @@ final class VersionStrategies {
             if (branchName != "master" && branchName != "develop") {
                 branchName = "$prefix.${branchName.toLowerCase()}"
             }
+
+            //Split at branch delimiter /-_+ and replace with .
             branchName = branchName.replaceAll(/((\/|-|_|\.)+)([\w])/) { all, delimiterAll, delimiter , firstAfter -> ".${firstAfter}" }
+            //Remove all hanging /-_+
+            branchName = branchName.replaceAll(/[-\/_\+]+$/) { "" }
+            //parse all digits and replace with unpadded value e.g. 001 -> 1
+            branchName = branchName.replaceAll(/([\w\.])([0-9]+)/) { all, s, delimiter ->
+                if(s == ".") {
+                    s = ""
+                }
+
+                "${s}.${Integer.parseInt(delimiter).toString()}"
+            }
 
             state.copyWith(inferredPreRelease: branchName)
         }