Avoid locale-dependent String.format for numbers

[A248]

Arabic numerals look like '١' instead of '1' and are used in some Arabic-speaking countries

String.format is locale-dependent, so it will produce these numbers, depending on the machine locale. This PR removes the use of String.format so that JFFI uses the correct string value for stubLibraryName.

Sample Error

Without this PR, running JFFI using an Arabic locale produces an error like this:

[ERROR] : could not get native definition for type `POINTER`, original error message follows: java.lang.UnsatisfiedLinkError: could not locate stub library in jar file.  Tried [jni/x86_64-Linux/libjffi-١.٢.so, /jni/x86_64-Linux/libjffi-١.٢.so]
[ERROR] 	at com.kenai.jffi.internal.StubLoader.getStubLibraryStream(StubLoader.java:589)
[ERROR] 	at com.kenai.jffi.internal.StubLoader.loadFromJar(StubLoader.java:444)
[ERROR] 	at com.kenai.jffi.internal.StubLoader.load(StubLoader.java:338)
[ERROR] 	at com.kenai.jffi.internal.StubLoader.<clinit>(StubLoader.java:626)