Make errors diffable

In the case of multiple errors in the same spec it just appends the errors

example

     Failure/Error: it { should contain_file(expected_filename).with_content(read_file("populated-mavenrc")) }
       expected that the catalogue would contain File[/home/u/.mavenrc] with content set to "export MAVEN_OPTS=\"-Xmx256m $MAVEN_OPTS\"\nexport PATH=\"/usr/local/bin:$PATH\"\necho Hello World!\ns\n" but it is set to "export MAVEN_OPTS=\"-Xmx256m $MAVEN_OPTS\"\nexport PATH=\"/usr/local/bin:$PATH\"\necho Hello World!\n"
       Diff:
       @@ -1,5 +1,4 @@
        export MAVEN_OPTS="-Xmx256m $MAVEN_OPTS"
        export PATH="/usr/local/bin:$PATH"
        echo Hello World!
       -an extra line