Fix typo

Author: Meinersbur

Diff for: flang/docs/FlangDriver.md

@@ -185,7 +185,7 @@ The automatically added libraries are:
 If the code is C/C++ based and invokes Fortran routines, one can either use Clang
 or Flang as the linker driver.  If Clang is used, it will automatically all
 required runtime libraries needed by C++ (e.g., for STL) to the linker invocation.
-In this case, one has to explicitly provide the Fortran runtime libraries
+In this case, one has to explicitly provide the Fortran runtime library
 `FortranRuntime`.  An alternative is to use Flang to link.
 In this case, it may be required to explicitly supply C++ runtime libraries.