guard against . not in path

Reference: /n/atom/patch/applied/runetypeinstfail
Date: Fri Apr  4 02:44:13 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/runetype/mkfile	Fri Apr  4 02:44:13 2014
+++ /sys/src/cmd/runetype/mkfile	Fri Apr  4 02:44:13 2014
@@ -4,7 +4,7 @@
 <|mkrunesize
 url=http://www.unicode.org/Public/UNIDATA/
 <|sed -n ''''s/^([A-Z])/cpu\1/p''''  </$cputype/mkfile
-uconv=$cpuO.uconv
+uconv=./$cpuO.uconv
 CLIB=/sys/src/libc/port
 ULIB=/lib
 BIN=/$objtype/bin/rune