Update 3.nebula-cpp-client.md

docs-2.0-en/14.client/3.nebula-cpp-client.md

@@ -63,7 +63,7 @@ This document describes how to install NebulaGraph CPP with the source code.
 
 5. Compile NebulaGraph CPP.
 
-  To speed up the compiling, use the `-j` option to set a concurrent number `N`. It should be $\min(\text{CPU}core number,\frac{the_memory_size(GB)}{2})$.
+  To speed up the compiling, use the `-j` option to set a concurrent number `N`. It should be $\min(\text{CPU core number},\frac{\text{the memory size(GB)}}{2})$.
 
   ```bash
   $ make -j{N}