Use export also in commented out variables.

Place the export command also on configuration lines that are
commented out, so that the user can easily uncomment those lines and
get the variable globally scoped.

See #54

bin/pgenv

@@ -2,7 +2,7 @@
 #
 # VERSION
 #
-PGENV_VERSION="1.3.0"
+PGENV_VERSION="1.3.1"
 
 # https://stackoverflow.com/a/19622569/79202
 trap 'exit' ERR
@@ -629,7 +629,7 @@ pgenv_configuration_write_variable(){
         if [ -z "$value" ]; then
             echo -n "#" >> "$file"
         fi
-        echo "${name}='${value}'" >> "$file"
+        echo "export ${name}='${value}'" >> "$file"
     fi
     echo >> "$file"
 }