ui: fix configwith doctest

4.2 cannot be expressed with IEEE floating point losslessly, and could
cause test failure on some platform:

    File ".../mercurial/ui.py", line 414, in mercurial.ui.ui.configwith
    Failed example:
        u.configwith(float, s, 'float2')
    Expected:
        -4.2
    Got:
        -4.2000000000000002

This patch fixes that by changing the number to 4.25, which can be expressed
by the binary number 100.01.

mercurial/ui.py

@@ -410,9 +410,9 b' class ui(object):'
         >>> u.setconfig(s, 'float1', '42')
         >>> u.configwith(float, s, 'float1')
         42.0
-        >>> u.setconfig(s, 'float2', '-4.2')
+        >>> u.setconfig(s, 'float2', '-4.25')
         >>> u.configwith(float, s, 'float2')
-        -4.2
+        -4.25
         >>> u.configwith(float, s, 'unknown', 7)
         7
         >>> u.setconfig(s, 'invalid', 'somevalue')