Fixed style - made convertStringToDoubleOrThrow static

Author: otethal

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/BuiltinConstructors.java

@@ -1014,7 +1014,7 @@ private double convertStringToDouble(VirtualFrame frame, String str, Object orig
 
         // Adapted from Jython PyString's atof() method
         @TruffleBoundary
-        private double convertStringToDoubleOrThrow(String str) throws NumberFormatException {
+        private static double convertStringToDoubleOrThrow(String str) throws NumberFormatException {
             StringBuilder s = null;
             int n = str.length();