Problem installing 0.14.5 with GCC 8.1

**Performed steps**

try to install the new openpmd-api release:

config:
```
openPMD build configuration:
library Version: 0.14.5
openPMD Standard: 1.1.0
C++ Compiler: GNU 8.1.0

```

led to the following output/problem during compilation

```
AbstractIOHandler.hpp:111:46: error: 'const openPMD::internal::FlushParams{InternalFlush}' is not a constant expression
constexpr FlushParams defaultFlushParams{};
^
```
Could this be linked to a too old GNU (8.1) compiler ?