Fix ruby 2.1 detection

diff --git a/lib/kross/configure.in.in b/lib/kross/configure.in.in
index 918588a..19c438e 100644
--- a/lib/kross/configure.in.in
+++ b/lib/kross/configure.in.in
@@ -36,9 +36,9 @@
         RUBY_CFLAGS=`$PKGCONFIG ruby --cflags`
       fi
       if test -z "$RUBY_VERSION"; then
-        RUBY_VERSION=`$PKGCONFIG ruby-1.9 --modversion 2>/dev/null`
+        RUBY_VERSION=`$PKGCONFIG ruby-2.1 --modversion 2>/dev/null`
         if test -n "$RUBY_VERSION"; then
-          RUBY_CFLAGS=`$PKGCONFIG ruby-1.9 --cflags`
+          RUBY_CFLAGS=`$PKGCONFIG ruby-2.1 --cflags`
         fi
       fi
       if test -z "$RUBY_VERSION"; then
@@ -48,6 +48,12 @@
         fi
       fi
       if test -z "$RUBY_VERSION"; then
+        RUBY_VERSION=`$PKGCONFIG ruby-1.9 --modversion 2>/dev/null`
+        if test -n "$RUBY_VERSION"; then
+          RUBY_CFLAGS=`$PKGCONFIG ruby-1.9 --cflags`
+        fi
+      fi
+      if test -z "$RUBY_VERSION"; then
         # pkgconfig file does not exist but might be 1.9.1: RUBY_VERSION defined in ruby/version.h
         if test -n "$RUBY -r rbconfig -e 'printf("%s",RbConfig::CONFIG@<:@"rubyhdrdir"@:>@)'"; then
           # rubyhdrdir parameter works only in >=1.9.1; this is 1.9.1