rune/libenclave/pal: fix the PAL version API description error in spec_v2.md

In enclave runtime PAL v2, the API of PAL version is named as pal_get_version
rather than pal_version.
Signed-off-by: NYilin Li <YiLin.Li@linux.alibaba.com>

rune/libenclave/internal/runtime/pal/spec_v2.md

 # Enclave Runtime PAL API Specification v2
 Enclave Runtime PAL API defines a common interface to interact between `rune` and enclave runtime.
 
-## 1.pal_version()
+## 1.pal_get_version()
 
 ### Description
 Indicate PAL API version number implemented by runelet and enclave runtime; runelet is compatible with any enclave runtimes equal to or less than the indicated value. If this symbol is undefined in enclave runtime, version 1 is assuemd by runelet.
 
 ### Prototype
 ```c
-int pal_version();
+int pal_get_version();
 ```
 
 ### Parameters