fix typo

doc/src/Howto_nemd.txt

@@ -26,7 +26,7 @@ the "fix ave/chunk"_fix_ave_chunk.html command.
 
 NOTE: A recent (2017) book by "(Daivis and Todd)"_#Daivis-nemd
 discusses use of the SLLOD method and non-equilibrium MD (NEMD)
-thermosttating generally, for both simple and complex fluids,
+thermostatting generally, for both simple and complex fluids,
 e.g. molecular systems.  The latter can be tricky to do correctly.
 
 As discussed in the previous section on non-orthogonal simulation