fetch-configlet uses slightly more portable syntax.

- fixes exercism/x-api#59

bin/fetch-configlet

 
 OS=$(
 case $(uname) in
-    Darwin*)
+    (Darwin*)
         echo "mac";;
-    Linux*)
+    (Linux*)
         echo "linux";;
-    Windows*)
+    (Windows*)
         echo "windows";;
-    *)
+    (*)
         echo "linux";;
 esac)
 
 ARCH=$(
 case $(uname -m) in
-    *64*)
+    (*64*)
         echo 64bit;;
-    *686*)
+    (*686*)
         echo 32bit;;
-    *386*)
+    (*386*)
         echo 32bit;;
-    *)
+    (*)
         echo 64bit;;
 esac)