Replace em-dash with ASCII in LinearGradientPaint comment

CI's "Java sources must be ASCII-only" guardrail flagged the em-dash that
slipped into the explanatory comment block.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: shai-almog

CodenameOne/src/com/codename1/ui/LinearGradientPaint.java

@@ -204,7 +204,7 @@ private void paint(Graphics g, double w, double h, boolean processCycles) {
         // baked them into `t2.translate(startX + tx, startY + ty)`, then
         // zeroed `g.translate(-tx, -ty)` before `g.setTransform(t2)`. On
         // ports where `isTranslationSupported()` is false (iOS, Android,
-        // JavaSE — every active port today), Graphics already conjugates
+        // JavaSE -- every active port today), Graphics already conjugates
         // setTransform with `T(xTranslate)` so the user matrix operates in
         // local coordinates regardless of prior g.translate; that
         // conjugation re-applies the cell offset at the *screen* level