Replace backslash with forward slash in f1_keywords metadata

[Rageking8]

The math/... entries in f1_keywords should use forward slash instead of backslash, as seen in some examples:

cpp-docs/docs/c-runtime-library/reference/isnan-isnan-isnanf.md

Line 9 in 6d9d959

f1_keywords: ["_isnan", "isnan", "math/isnan", "math/_isnan", "math/_isnanf", "_isnanf"]

cpp-docs/docs/c-runtime-library/reference/atof-atof-l-wtof-wtof-l.md

Line 9 in 6d9d959

f1_keywords: ["_tstof", "_ttof", "atof", "stdlib/atof", "math/atof", "_atof_l", "stdlib/_atof_l", "math/_atof_l", "_wtof", "corecrt_wstdlib/_wtof", "_wtof_l", "corecrt_wstdlib/_wtof_l"]

cpp-docs/docs/c-runtime-library/reference/fmin-fminf-fminl.md

Line 9 in 6d9d959

f1_keywords: ["fmin", "fminf", "fminl", "math/fmin", "math/fminf", "math/fminl"]

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