Fix solution/project files for nested directories.

By having the leading `/` infront of the `*` makes these types of files relative to the directory the gitignore is in. If you create a Unity project inside of a git directory Unity forces you to create a new directory, thus not picking up these files.

Unity.gitignore

@@ -4,14 +4,14 @@
 [Bb]uild/
 
 # Autogenerated VS/MD solution and project files
-/*.csproj
-/*.unityproj
-/*.sln
-/*.suo
-/*.user
-/*.userprefs
-/*.pidb
-/*.booproj
+*.csproj
+*.unityproj
+*.sln
+*.suo
+*.user
+*.userprefs
+*.pidb
+*.booproj
 
 #Unity3D Generated File On Crash Reports
 sysinfo.txt