use US locale to format strings

This is especially important for all strings that are
passed to gnuplot. Because gnuplot uses the US locale
during parsing.

pdb-plotting/src/main/java/org/lucares/recommind/logs/AxisSettings.java

@@ -1,6 +1,7 @@
 package org.lucares.recommind.logs;
 
 import java.util.List;
+import java.util.Locale;
 
 import org.apache.commons.lang3.StringUtils;
 
@@ -162,7 +163,7 @@ public class AxisSettings {
     }
 
     private void appendfln(final StringBuilder builder, final String format, final Object... args) {
-        builder.append(String.format(format + "\n", args));
+        builder.append(String.format(Locale.US, format + "\n", args));
     }
 
     @Override

pdb-plotting/src/main/java/org/lucares/recommind/logs/Plotter.java

@@ -10,6 +10,7 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Locale;
 import java.util.UUID;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -209,7 +210,7 @@ public class Plotter {
 
         final int values = csvSummary.getValues();
         result.append(" (");
-        result.append(String.format("%,d", values));
+        result.append(String.format(Locale.US, "%,d", values));
         result.append(")");
 
         return result.toString();