Use the smallest available flash& ram size

Build as release so we can be sure they fit

.travis.yml

@@ -15,4 +15,4 @@ matrix:
   fast_finish: true
 script:
   - rustup target add thumbv6m-none-eabi
-  - cargo build --features=$MCU --examples
+  - cargo build --features=$MCU --examples --release

memory.x

@@ -1,8 +1,8 @@
 MEMORY
 {
   /* NOTE K = KiBi = 1024 bytes */
-  FLASH : ORIGIN = 0x08000000, LENGTH = 32K
-  RAM : ORIGIN = 0x20000000, LENGTH = 6K
+  FLASH : ORIGIN = 0x08000000, LENGTH = 16K
+  RAM : ORIGIN = 0x20000000, LENGTH = 4K
 }
 
 /* This is where the call stack will be allocated. */