remove absolute path from contrib/package_nsis-mingw.sh in order to make it easier to automatically build tor expert bundle

changes/win-bundle-path

@@ -0,0 +1,4 @@
+  o Packaging changes:
+    - Remove absolute path from makensis.exe command to build Tor expert bundle
+      in order to make it easier to automate package builds
+

contrib/package_nsis-mingw.sh

@@ -91,5 +91,5 @@ clean_localstatedir src/config/torrc.sample.in win_tmp/src/config/torrc.sample
 cp contrib/tor-mingw.nsi.in win_tmp/contrib/
 
 cd win_tmp
-"C:\Program Files\NSIS\makensis.exe" contrib/tor-mingw.nsi.in
+makensis.exe contrib/tor-mingw.nsi.in