Make GoLangMatchFileFilter work on Windows

Without this,
BuildImageCmdImplTest.testDockerBuilderAddFolder()
and BuildImageCmdImplTest.testDockerIgnore() both fail with

java.util.regex.PatternSyntaxException: Illegal/unsupported escape
sequence near index 3
D:\Eclipse\Jenkins\docker-java\target\test-classes\testDockerignore\a\
   ^
	at java.util.regex.Pattern.error(Pattern.java:1924)
	at java.util.regex.Pattern.escape(Pattern.java:2416)
	at java.util.regex.Pattern.atom(Pattern.java:2164)
	at java.util.regex.Pattern.sequence(Pattern.java:2097)
	at java.util.regex.Pattern.expr(Pattern.java:1964)
	at java.util.regex.Pattern.compile(Pattern.java:1665)
	at java.util.regex.Pattern.<init>(Pattern.java:1337)
	at java.util.regex.Pattern.compile(Pattern.java:1022)
	at java.lang.String.replaceFirst(String.java:2119)
	at
com.github.dockerjava.core.GoLangMatchFileFilter.accept(GoLangMatchFileFilter.java:26)
	at
org.apache.commons.io.filefilter.AndFileFilter.accept(AndFileFilter.java:122)
	at
org.apache.commons.io.filefilter.OrFileFilter.accept(OrFileFilter.java:118)
	at java.io.File.listFiles(File.java:1285)