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.
# 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
