Fix TypeError in `crew const` when a value is nil (#4981)

crew

@@ -315,7 +315,7 @@ end
 def const (var)
   if var
     value = eval(var)
-    puts var + '=' + value
+    puts "#{var}=#{value}"
   else
     vars = [
       'ARCH',
@@ -349,7 +349,7 @@ def const (var)
     ]
     vars.each { |var|
       value = eval(var)
-      puts var + '=' + value
+      puts "#{var}=#{value}"
     }
   end
 end

lib/const.rb

 # Defines common constants used in different parts of crew
 
-CREW_VERSION = '1.5.10'
+CREW_VERSION = '1.5.11'
 
 ARCH_ACTUAL = `uname -m`.strip
 # This helps with virtualized builds on aarch64 machines