"provided" scope dependencies are missed during generation

While the mojo specifies `requiresDependencyResolution = COMPILE_PLUS_RUNTIME` only uses runtime dependencies (via `project.getRuntimeClasspathElements()`). getRuntimeClasspathElements filters dependencies by:

```java
if ( Artifact.SCOPE_COMPILE.equals( a.getScope() ) || Artifact.SCOPE_RUNTIME.equals( a.getScope() ) )
```

It should instead be calling `project.getCompileClasspathElements` which filters by:

```java
if ( Artifact.SCOPE_COMPILE.equals( a.getScope() ) || Artifact.SCOPE_PROVIDED.equals( a.getScope() ) ||
                    Artifact.SCOPE_SYSTEM.equals( a.getScope() ) )
```

Which includes `<scope>provided</scope>` dependencies.

I've tested this on a simple web project where `javax.servlet:javax.servlet-api` breaks the current 1.2.0 version) and confirmed that this works with this patch.

Not sure if there's a meaningful unit test that can be added to support this (given it requires a whole separate project, etc).

M