Fix comment in linear_expr.h
Fix comment in linear_expr.h

or-tools/or-tools,or-tools/or-tools,or-tools/or-tools,or-tools/or-tools,google/or-tools,or-tools/or-tools,google/or-tools,google/or-tools,google/or-tools,google/or-tools,google/or-tools,or-tools/or-tools