JS: Make docs match reality

Author: asger-semmle

javascript/extractor/src/com/semmle/js/ast/Position.java

@@ -15,7 +15,7 @@ public int getLine() {
     return line;
   }
 
-  /** The column number (1-based) of this position. */
+  /** The column number (0-based) of this position. */
   public int getColumn() {
     return column;
   }